Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.91.074713

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We performed ultrasonic measurements on (Ta0.952V0.048)(2)NiSe5 to investigate the contribution of acoustic phonons at the zone center to structural and possible excitonic transitions. The transverse elastic constant C-55 with irreducible representation B-2g exhibits softening over 90% above a transition temperature of T-s = 280 K, indicating the soft mode of corresponding TA phonons. Our analysis based on the quadrupole response indicates that the electron-phonon interaction contributes to the excitonic transition in addition to the hybridization between the conduction and valence bands if the excitonic transition is realized.

DOI： 10.7566/JPSJ.91.024601

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.103.014511

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.014511/fulltext

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Temperature dependence of the In-115-NMR spectra of CeRhIn5 is studied with the external magnetic fields 10 degrees off the [100] and [001] axes. Our detailed analyses confirm that the AFM3 phase breaks the four-fold spin symmetry with the commensurate ordering vector of Q = (0. 5, 0.5, 0.25). Based on the observation of anistropic hyperfine fields, we also propose the symmetry lowering of the electronic structure in the AFM3 phase.

DOI： 10.7566/JPSJ.89.094709

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We performed an ultrasonic measurement for the heavy-fermion compound CeRhIn_5 to investigate the origin of the field-induced anisotropic phase in high magnetic fields. The transverse elastic constant C_T=(C_{11}−C_{12})/2 and the ultrasonic attenuation coefficient αT show clear anomaly at B^★=28.5T, which was discussed as the electronic nematic transition point. In addition, C_T exhibits acoustic de Haas-van Alphen oscillation below 28.5 T. These elastic anomalies around B★ indicate an electric quadrupole ordering of O_{x^2−y^2} accompanied by B_{1g} crystal symmetry breaking and Fermi surface reconstruction due to the quadrupole-strain coupling, which results from itinerant 4f electrons and the p−f hybridized state.

DOI： 10.1103/PhysRevB.101.155125

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.30.011122

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2020.1.0_1750

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DOI： 10.1103/PHYSREVB.101.195146

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We studied the pressure effect up to 8 GPa on antiferromagnet CeAl by means of ac specific heat C-ac, ac susceptibility chi', and electrical resistivity rho. and constructed temperature-pressure phase diagram. CeAl undergoes an antiferromagnetic (AFM) ordering at T-N1 similar to 10 K at ambient pressure, which is changed to three successive AFM transition temperatures (T-N2, T-N3, T-N4) above 1.7 GPa. AFM transition temperatures attain a maximum at 6.0 GPa and seem to vanish at P* = 7.5 GPa. A pressure induced phase, which emerges above 4.5 GPa, is also developed around P*. We analyzed low temperature resistivity in order to study quantum criticality around P*.

DOI： 10.7566/JPSJ.88.034707

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Publisher：{AIP} Publishing  

DOI： 10.1063/1.5043138

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

In most strongly correlated electron systems superconductivity appears nearby a magnetic quantum critical point (QCP) which is believed to cause unconventional behaviors. In order to explore this physics, we present here a study of the heavy-fermion superconductors CeIrSi3 and CeRhSi3 carried out using a newly developed system for high-resolution magnetic penetration-depth measurements under pressure. Superconductivity in CeIrSi3 shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi3 does not possess a T=0 quantum phase transition and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that in these compounds unconventional superconducting behaviors are rather connected with the coexisting antiferromagnetic order. This study provides another viewpoint on the interplay of superconductivity, magnetism, and quantum criticality in CeIrSi3 and CeRhSi3 and maybe in other heavy fermions.

DOI： 10.1103/PhysRevB.97.104513

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.1.0_1513

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report measurements of the de Haas-van Alphen effect in the layered heavy-fermion compound CePt2In7 in high magnetic fields up to 35 T. Above an angle-dependent threshold field, we observed several de Haas-van Alphen frequencies originating from almost ideally two-dimensional Fermi surfaces. The frequencies are similar to those previously observed to develop only above a much higher field of 45 T, where a clear anomaly was detected and proposed to originate from a change in the electronic structure [M. M. Altarawneh et al., Phys. Rev. B 83, 081103 (2011)]. Our experimental results are compared with band structure calculations performed for both CePt2In7 and LaPt2In7, and the comparison suggests localized f electrons in CePt2In7. This conclusion is further supported by comparing experimentally observed Fermi surfaces in CePt2In7 and PrPt2In7, which are found to be almost identical. The measured effective masses in CePt2In7 are only moderately enhanced above the bare electron mass m(0), from 2m(0) to 6m(0).

DOI： 10.1103/PhysRevB.96.075138

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The 4f crystalline electric field (CEF) of the Pr3+ ion of PrPt2Cd20 with a cubic crystal structure has been studied by measuring its high-field magnetization up to 45 T, specific heat in a wide temperature range in magnetic fields, and electrical resistivity. Magnetization curves for the magnetic field along the [100] and [110] directions show metamagnetic-like features at approximately 1.5 and 15 T, respectively. The specific heat shows a Schottky peak centered at 2.4 K. These experimental results were explained well by the CEF scheme with the non-Kramers Gamma(3) doublet ground state with a small overall CEF splitting energy of about 40 K. The specific heat also shows another broad peak below 1K with an associated entropy release of R ln 2. This peak was interpreted by a split of the Gamma(3) doublet ground state with an energy of Delta = 0.4 K. These results suggest that the local symmetry of the Pr site is lowered from a cubic one. The possible reasons for this symmetry lowering are discussed.

DOI： 10.7566/JPSJ.86.074711

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

We report on superconducting nature under pressure in CeIr(In1-xCdx)5 by In-Nuclear-Quadrupole-Resonance (NQR) studies. In CeIr(In0.925Cd0.075)5, the inhomogeneous antiferromagnetic order at TN ∼ 2.3 K is induced by Cd-dopants and superconductivity disappears at ambient pressure. However, the measurements of a nuclear-spin-lattice-relaxation rate 1/T1 have revealed that the superconductivity suddenly occurs above 2.1 GPa. It is observed that the superconducting gap is enhanced in the Cd-doped sample, indicating that the Cd-doping induces the strong coupling superconductivity leading to the enhancement of Tc in the CeIrIn5 system. Furthermore, we found that the residual density of states at the Fermi level increases with increasing pressure, suggesting that the superconducting nature of CeIrIn5 is quite different from those of CeCoIn5 and CeRhIn5.

DOI： 10.1088/1742-6596/807/5/052004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The magnetic structure of the heavy fermion antiferromagnet CePt2In7 is determined using neutron diffraction. We find a magnetic wave vector q(M) = (1/2,1/2,1/2), which is temperature independent up to T-N = 5.5 K. A staggered moment of 0.45(1)mu(B) at 2 K resides on the Ce ion. The nearest-neighbor moments in the tetragonal basal plane are aligned antiferromagnetically. The moments rotate by 90 degrees. from one CeIn3 plane to another along the c axis. A much weaker satellite peak with an incommensurate magnetic wave vector q(M) = (1/2,1/2,0.47) seems to develop at low temperature. However, the experimental data available so far are not sufficient to draw a definitive conclusion about the possible coexistence of commensurate and incommensurate magnetic structures in this material.

DOI： 10.1103/PhysRevB.95.161102

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

We succeeded in growing five new single crystalline compounds RPt2Cd20 (R = La, Ce, Pr, Nd, and Sm) by the Cd self-flux method. These compounds are found to crystallize in the cubic CeCr2Al20-type crystal structure by the X-ray diffraction using single crystals. We measured the electrical resistivity, magnetic properties, and specific heat for all compounds. The resistivity for R = Ce, Nd, and Sm indicates an abrupt decrease, which might correspond to a magnetic transition. It is suggested that the ground state of CePt2Cd20 is Gamma(7) doublet from the magnetization measurement. The magnetization of PrPt2Cd20 shows a metamagnetic behavior at 1.6 T in the paramagnetic state, which could be due to the crystalline electric field effect with non-Kramers Gamma(3) doublet or Gamma(1) singlet ground state. The contribution of optical phonon modes to the lattice specific heat is discussed in LaPt2Cd20. (C) 2016 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jallcom.2016.09.077

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Using novel instrumentation to combine extreme conditions of intense pulsed magnetic field up to 60 T and high pressure up to 4 GPa, we have established the three-dimensional (3D) magnetic field-pressure-temperature phase diagram of a pure stoichiometric heavy-fermion antiferromagnet (CeRh2Si2). We find a temperature and pressure-dependent decoupling of the critical and pseudometamagnetic fields at the borderlines of antiferromagnetism and strongly-correlated paramagnetism. This 3D phase diagram is representative of a class of heavy-fermion Ising antiferromagnets, where long-range magnetic ordering is decoupled from a maximum in the magnetic susceptibility. The combination of extreme conditions enabled us to characterize different quantum phase transitions, where peculiar quantum critical properties are revealed. The interest to couple the effects of magnetic field and pressure on quantum-critical correlated-electron systems is stressed.

DOI： 10.1103/PhysRevB.95.014411

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

High-magnetic-field X-ray absorption spectroscopy of the heavy-fermion compound CeIrIn5 has been conducted to clarify the valence state of Ce at the metamagnetic transition. The field-induced change in the X-ray absorption spectrum near the Ce-L-3 edge is found to be smaller than the resolution limit of the measurement, suggesting that no field-induced valence change larger than 0.005 takes place at 2K up to 42 T.

DOI： 10.7566/JPSJ.85.115001

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Language：English   Publisher：IOP PUBLISHING LTD  

We review the nature of strongly correlated electronic states in rare earth and actinide compounds, focusing on localized versus itinerant electronic states in CeRhIn5, quantum critical phenomena in YbIr2Zn20, residual resistivity in CeCu6, metamagnetism in heavy fermion compounds, and unconventional superconductivity in CeIrSi3 without inversion symmetry in the crystal structure, emphasizing that sample quality is essentially important to clarify the characteristic features for the heavy fermion compounds.

DOI： 10.1088/0034-4885/79/11/114501

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We succeeded in growing a new high quality single crystal of a ternary uranium compound UPd2Cd20. From the electrical resistivity, magnetization, magnetic susceptibility, and specific heat experiments, UPd2Cd20 is found to be an antiferromagnetic heavy-fermion compound with the Neel temperature T-N = 5 K and exhibits the large electronic specific heat coefficient. exceeding 500 mJ (K-2.mol)(-1). This compound is the first one that exhibits the magnetic ordering with the magnetic moments of the U atom in a series of UT2X20 (T: transition metal, X = Al, Zn, Cd). UPd2Cd20 shows typical characteristic features in heavy-fermion systems such as a broad maximum in the magnetic susceptibility at T-chi max and a large coefficient A of T-2 term in the resistivity.

DOI： 10.1088/0953-8984/28/42/425601

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

A diffraction experiment using high-energy X-rays was carried out on YbInCu4. Below the Yb valence transition temperature, the splitting of Bragg peaks was detected in high-order reflections. No superlattice reflections accompanying the valence ordering were found below the transition temperature. These experimental findings indicate that a structural change from a cubic structure to a tetragonal structure without valence ordering occurs at the transition temperature. Such a structural change free from any valence ordering is difficult to understand only in terms of Yb valence degrees of freedom. This means that the structural change may be related to electronic symmetries such as quadrupolar degrees of freedom as well as to the change in Yb valence.

DOI： 10.7566/JPSJ.85.063602

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The magnetization change Delta M at the superconducting transition of LaIrSi3 has been measured in various magnetic fields H. The observed Delta M in H = 0 is within the range of the Meissner effect induced by the possible residual field, suggesting that the spontaneous magnetization, if it exists, is below the experimental accuracy. This result is in agreement with the results of mu SR experiments, in which no spontaneous magnetic field has been observed in the superconducting state.

DOI： 10.7566/JPSJ.85.025002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We present a new specially designed pressure cell and technique adapted for resistivity measurements in pulsed magnetic fields up to 60 T at pressures up to at least 4 GPa, and temperatures down to 1.5 K. We show that heating effects during the pulse are acceptable (less than 1 K) and can be corrected allowing reliable temperature dependences of the magnetoresistance to be obtained. We illustrate the performance with a study of the phase diagram of the heavy fermion antiferromagnet CeRh2Si2. (C) 2016 AIP Publishing LLC.

DOI： 10.1063/1.4941714

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report specific heat measurements on a high-quality single crystal of the heavy-fermion compound CePt2In7 in magnetic fields up to 27 T. The zero-field specific heat data above the Neel temperature, T-N, suggest a moderately enhanced value of the electronic specific heat coefficient gamma = 180 mJ/K-2 mol. For T < T-N, the data at zero applied magnetic field are consistent with the existence of an anisotropic spin-density wave opening a gap on almost the entire Fermi surface, suggesting extreme two-dimensional electronic and magnetic structures for CePt2In7. T-N is monotonically suppressed by magnetic field applied along the c axis. When a field is applied parallel to the a axis, T-N first increases at low field up to about 10 T and then decreases monotonically at a higher field. The magnetic phase diagram based on specific heat measurements suggests that a field-induced quantum critical point is likely to occur slightly below 60 T for both principal orientations of the magnetic field.

DOI： 10.1103/PhysRevB.93.085121

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have measured the magnetization of two noncentrosymmetric superconductors: Ir2Ga9 and CePt3Si using a SQUID magnetometer, neither of which has been tested for the time-reversal symmetry in the superconducting state. For Ir2Ga9, the magnetization change Delta M below the superconducting transition temperature T-c similar to 2.2 K was smaller than 10(-5) G in zero magnetic field, suggesting that Delta M originates in the Meissner effect induced by the possible residual field. When CePt3Si was cooled in zero magnetic field, Delta M along the c axis first decreased below T-c(+) similar to 0.75 K (high-T-c phase) and then increased below T-c(-) similar to 0.45 K (bulk superconducting phase). Since this behavior cannot be explained by the Meissner effect, it may be a sign of a spontaneous magnetization.

DOI： 10.1088/1742-6596/683/1/012029

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_2100

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DOI： 10.11316/jpsgaiyo.71.1.0_2013

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DOI： 10.11316/jpsgaiyo.71.1.0_2439

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Crossover phase diagrams in the magnetic field versus temperature (H-T) plane of the nonmagnetic heavy-fermion metamagnets UT2Zn20 (T:Ir, Co) are studied by measuring the magnetic and electronic transport properties. The crossover phase diagrams of UIr2Zn20 and UCo2Zn20 are composed of a low-magnetic-field region (LFR) and a high-magnetic-field region (HFR), which are characterized by magnetic properties and the Hall effect, respectively. The LFR is found to form a closed area in the H-T plane, which is a quite different feature from the conventional uranium heavy-fermion compounds and the first observation in uranium compounds. From the drastic anomaly in the Hall effect at a metamagnetic field of UIr2Zn20, it is found that the metamagnetic behavior in UIr2Zn20 corresponds to a crossover from the heavy-fermion state to the field-induced ferromagnetic or polarized paramagnetic state accompanied by the reconstruction or topology change of Fermi surfaces. In UCo2Zn20, on the other hand, no sign of abrupt change in the electronic state at the metamagnetic field is observed. These contrastive crossover phase diagrams and the electronic state changes at the metamagnetic field are due to the different hybridization strengths between the 5 f electrons of U atoms and the d electrons of Ir and Co atoms, leading to the differences in magnetic correlation and crystalline electric field ground state or the degree of itinerancy of 5 f electrons.

DOI： 10.7566/JPSJ.84.074704

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We report magnetization of a non-centrosymmetric superconductor, LaPt3Si below 0.6 K up to 200 Oe. The home-made SQUID and Hall sensor magnetometers that operate below 1 K were constructed for this purpose. Although the SQUID magnetometer is more sensitive than the Hall sensor's one, it was found not to work correctly for the rapid magnetization change of LaPt3Si below 0.4 K. The Hall sensor magnetometer, in contrast, can properly detect magnetization jumps in the M-H curve of the superconducting state. The observed flux jumps are probably related to the interfusion of the mixed state of the LaPt3Si that is observed in the mu SR measurements. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.048001

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De Haas-van Alphen experiments were performed on the valence fluctuation compound YbCu2Si2. For the field direction close to the c-axis in the tetragonal structure, a very large cyclotron effective mass of 43m(0) was detected on branch beta, which corresponds to the nearly cylindrical Fermi surface. This mass is one of the largest cyclotron masses detected experimentally in Yb compounds.

DOI： 10.7566/JPSJ.84.035002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have measured the magnetization of single crystals of the non-centrosymmetric superconductor LaNiC2, which is considered to break time-reversal symmetry by mu SR measurements. Below the transition temperature T-c similar to 3K, the emergence of magnetization on the order of 10(-5) G is observed in zero magnetic field along the c-axis but not along the a-axis. This spontaneous magnetization is larger than the Meissner effect induced by the possible residual field and did not change after applying magnetic fields of up to 15 mOe or after warming to room temperature. The results that the direction is related to the lack of inversion symmetry and that the magnitude is sensitive to the crystallinity of the sample suggest some analogy with pyroelectricity.

DOI： 10.7566/JPSJ.84.013702

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

We succeeded in growing single crystals of UPd2Cd20 by the Cd self-flux method. This compound crystallizes in the cubic CeCr2Al20-type structure. From the low-temperature electrical resistivity and Kadowaki-Woods relation, the electronic specific heat coefficient. is estimated to be about 400 mJ/mol . K-2. The magnetic susceptibility of UPd2Cd20 indicates a broad maximum at 6.6 K and a rapid decrease at 5.0 K, which correspond to the formation of the heavy fermion state and the antiferromagnetic transition, respectively. These experimental results strongly suggest that UPd2Cd20 is a new heavy fermion antiferromagnet.

DOI： 10.1016/j.phpro.2015.12.009

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YbT2Zn20 (T: Rh and Ir), which crystallizes in the cubic CeCr2Al20-type structure, is a member of the well-known heavy fermion compounds, indicating a huge electronic specific heat coefficient gamma similar or equal to 500 mJ/(K-2.mol). We have measured temperature and magnetic field dependences of Yb valence in YbT2Zn20(T: Rh and Ir) at ambient pressure by the L-III edge x-ray absorption spectroscopy in order to investigate the valence state of Yb 4f electrons in these compounds. It is revealed that the Yb valence in both compounds significantly decreases with temperature below about 100 K and increases with increasing magnetic field at low temperatures in contrast to the case of YbCo2Zn20.

DOI： 10.1088/1742-6596/592/1/012021

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We succeeded in growing single crystals of tetragonal RCu9Sn4 (R=La, Ce, Pr, and Eu) by the Sn-self-flux method for the first time, and studied the electrical and magnetic properties of these compounds. The magnetism of CeCu9Sn4 and PrCu9Sn4 indicates an Ising anisotropy with the magnetic easy axis parallel to the [001] direction. We revealed that EuCu9Sn4 shows an antiferromagnetic transition with an easy plane type magnetic anisotropy in the present single crystal study.

DOI： 10.1088/1742-6596/592/1/012034

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CePt2In7 is an antiferromagnet with T-N = 5.4 K, which shows pressure-induced superconductivity at transition temperature T-c = 2.1K around a critical pressure P-c = 3.2GPa. We have investigated an anisotropy of the superconducting upper critical field H-c2 in CePt2In7, which posesses two-dimensional tetragonal crystal structure and cylindrical Fermi surfaces elongated along c-axis. At 2.60GPa, initial slope of Hc(2) for H parallel to [001] is smaller than that for H parallel to [100], reflecting the two-dimensional Fermi surface of CePt2In7. However, Pauli paramagnetic suppression is strong for H parallel to [100] compared with that for H parallel to [001] in high magnetic field, and Hc(2)(0) for H parallel to [001] seems to be larger than that for H parallel to [100] at 2.60GPa in CePt2In7.

DOI： 10.1088/1742-6596/592/1/012006

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© 2015 The Authors. Published by Elsevier B.V. Precise thermal expansion and magnetostriction measurements were performed on the heavyfermion compound YbAuCu4 in order to examine the crossover valence transition at TV which was proposed by the nuclear magnetic resonance measurements. The temperature dependence of the thermal expansion coefficient α under magnetic fields shows a broad peak, which shifts to higher temperatures with increasing magnetic fields. The corresponding linear thermal expansion Δℓ/ℓ parallel to the magnetic field of 7.0 T shows a marked decrease below about 10 K, indicating a contraction of sample length at low temperatures. These results are discussed in relation to the observed temperature dependence of the nuclear quadrupole frequency νQ under magnetic fields.

DOI： 10.1016/j.phpro.2015.12.057

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Precise thermal expansion and magnetostriction measurements were performed on the heavy-fermion compound YbAuCu4 in order to examine the crossover valence transition at T-v which was proposed by the nuclear magnetic resonance measurements. The temperature dependence of the thermal expansion coefficient a under magnetic fields shows a broad peak, which shifts to higher temperatures with increasing magnetic fields. The corresponding linear thermal expansion Delta l/l parallel to the magnetic field of 7.0 T shows a marked decrease below about 10 K, indicating a contraction of sample length at low temperatures. These results are discussed in relation to the observed temperature dependence of the nuclear quadrupole frequency nu(Q) under magnetic fields.

DOI： 10.1016/j.phpro.2015.12.057

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© 2015 The Authors. Published by Elsevier B.V. We succeeded in growing single crystals of UPd2Cd20 by the Cd self-flux method. This compound crystallizes in the cubic CeCr2Al20-type structure. From the low-temperature electrical resistivity and Kadowaki-Woods relation, the electronic specific heat coefficient γ is estimated to be about 400mJ/mol ·K2. The magnetic susceptibility of UPd2Cd20 indicates a broad max-imum at 6.6K and a rapid decrease at 5.0K, which correspond to the formation of the heavy fermion state and the antiferromagnetic transition, respectively. These experimental results strongly suggest that UPd2Cd20 is a new heavy fermion antiferromagnet.

DOI： 10.1016/j.phpro.2015.12.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER  

The de Haas-van Alphen effect, which is a powerful method to explore Fermi surface properties, has been observed in cerium, uranium, and nowadays even in neptunium and plutonium compounds. Here, we present the results of several studies concerning the Fermi surface properties of the heavy fermion superconductors UPt3 and NpPd5Al2, and of the ferromagnetic pressure-induced superconductor UGe2, together with those of some related compounds for which fascinating anisotropic superconductivity, magnetism, and heavy fermion behavior has been observed. (C) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

DOI： 10.1016/j.crhy.2014.06.005

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DOI： 10.7566/JPSCP.3.011094

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DOI： 10.7566/JPSCP.3.012026

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DOI： 10.7566/JPSCP.3.011017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We studied the heavy fermion compound YbCo2Zn20 with an electronic specific heat coefficient gamma similar or equal to 8000 mJ/(K-2.mol) by measuring the de Haas-van Alphen (dHvA) oscillation, Hall effect, magnetic susceptibility, and magnetization at ambient pressure, as well as the electrical resistivity in magnetic fields of up to 320 kOe and at pressures of up to 5 GPa. The detected Fermi surfaces are small in volume, reflecting the small Brillouin zone based on the large cubic lattice constant a = 14.005 angstrom. The cyclotron effective masses, which were determined from the dHvA experiment, are found to be markedly reduced in magnetic fields. In other words, the detected cyclotron masses of 2.2-8.9 m(0) (m(0): the rest mass of an electron) at H-av = 117 kOe are enhanced to 100-500 m(0) at 0 kOe. By applying pressure, the heavy fermion state disappears at P-c similar or equal to 1.8 GPa and orders antiferromagnetically for P > P-c. The field-induced antiferroquadrupolar phase, which is observed only for H parallel to < 111 > in the magnetic field range from H-Q = 60 kOe to H-Q' = 210 kOe, is found to shift to lower magnetic fields and merge with theantiferromagnetic phase at 4.5 GPa.

DOI： 10.7566/JPSJ.83.044703

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In order to combine the extreme conditions of high pressure and magnetic field, we have developed a non-metallic diamond anvil cell to avoid Joule-heating in a pulsed-magnetic field. Although the cell is deformed with loading, a maximum pressure of ∼ 8.5 GPa can be applied. Quantum oscillation measurements using tunnel diode oscillator have been performed for heavy fermion antiferromagnet CePt2In7 in a pulsed field and at ambient pressure. The detail of the pressure cell and field-induced Fermi surface changes of CePt2In7 are discussed.

DOI： 10.1088/1742-6596/592/1/012149

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We grew a high-quality single crystal EuGa4 with the tetragonal structure by the Ga self-flux method, and measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, thermoelectric power and de Haas-van Alphen (dHvA) effect, together with the electrical resistivity and thermoelectric power under pressure. EuGa4 is found to be a Eu-divalent compound without anisotropy of the magnetic susceptibility in the paramagnetic state and to reveal the same magnetization curve between H ∥ [100] and [001] in the antiferromagnetic state, where the antiferromagnetic easy-axis is oriented along the [100] direction below a Néel temperature TN = 16:5 K. The magnetization curve is discussed on the basis of a simple two-sublattice model. The Fermi surface in the paramagnetic state was clarified from the results of a dHvA experiment for EuGa4 and an energy band calculation for a non-4f reference compound SrGa4, which consists of a small ellipsoidal hole-Fermi surface and a compensated cube-like electron-Fermi surface with vacant space in center. We observed an anomaly in the temperature dependence of the electrical resistivity and thermoelectric power at TCDW = 150K under 2 GPa. This might correspond to an emergence of the charge density wave (CDW). The similar phenomenon was also observed in EuAl4 at ambient pressure. We discussed the CDW phenomenon on the basis of the present peculiar Fermi surfaces. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.104703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

The f-electron system in rare-earth and actinide compounds exhibit a variety of characteristic properties including heavy fermions and unconventional superconductivity. The Fermi surface properties in rare-earth and actinide compounds are clarified by the de Haas-van Alphen experiments on the basis of the results of energy band calculations. The effect of pressure on the electronic states of CeRhIn5, CeIrSi3, and YbIr2Zn20 is studied in magnetic fields. An electronic instability, including unconventional superconductivity, occurs at 2.4 GPa in CeRhIn5 and 2.6 GPa in CeIrSi3. An abrupt non-linear increase in the magnetization, namely, a metamagnetic behavior, is found in the heavy fermion compounds, including YbT2Zn20 (T: Co, Rh, Ir). A super-heavy fermion state with a specific heat coefficient of 10 J/(K-2 center dot mol) is realized in YbIr2Zn20 under pressure.

DOI： 10.3938/jkps.63.409

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We measured the magnetic susceptibility, high-field magnetization, magnetoresistance, specific heat, and Hall coefficient, together with the electrical resistivity under high pressures and magnetic fields, for the heavy-fermion compound YbRh2Zn20 with the cubic CeCr2Al20-type structure. The metamagnetic behavior was observed at H-m = 65 kOe for the magnetic field along the (100) direction below T-Xmax = 5.3 K, at which the temperature of the magnetic susceptibility indicates a broad maximum. The coefficient A of the T-2 dependence of electrical resistivity rho = rho(0) + AT(2) and the electronic specific heat coefficient C/T possess a broad maximum at H-m. The metamagnetic field H-m is found to decrease with increasing pressure and to become zero at a critical pressure P-c similar or equal to 5.2 GPa. Correspondingly, the A value increases drastically in magnitude, and the Fermi liquid relation is no longer satisfied at 5.2 GPa in zero magnetic field, implying a non-Fermi liquid state. On the other hand, at magnetic fields of H > 20 kOe, the low-temperature resistivity exhibits a T-2 dependence even at 5.2 GPa. The A coefficient decreases rapidly with increasing magnetic field. These results indicate that an electronic state at 5.2 GPa corresponds to the quantum critical point.

DOI： 10.7566/JPSJ.82.084705

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

We measured the electrical resistivity of CeCu2Ge2 under various high pressures and strong magnetic fields. Beyond the previous antiferromagnetic critical pressure P (c) similar to 8 GPa, the antiferromagnetic phase is found to exist at much higher pressure of 10.9 GPa even in magnetic fields up to 8 T. The pressure vs. temperature phase diagram and the magnetic field vs. temperature phase diagram under high pressure were constructed. The pressure-induced antiferromagnetic phase is still observed and coexists with pressure-induced superconductivity at 10.9 GPa.

DOI： 10.3938/jkps.63.345

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We succeeded in growing single crystals of YbTIn 5 (T: Co, Rh, Ir), YbGa 4 , YbT 2 Zn 20 (T: Co, Rh, Ir), YbPdGe, Yb 2 Pt 2 Pb, and YbPd 5 Al 2 . The electronic and magnetic properties are clarified by measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat and de Haas - van Alphen effect. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.62.1858

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have investigated quadrupole effects in tetragonal crystals of PrCu2Si2 and DyCu2Si2 by means of low-temperature ultrasonic measurements. The elastic constant C-44 of PrCu2Si2 exhibits pronounced softening below 70 K down to a Neel temperature T-N = 20 K, which is described in terms of a quadrupole susceptibility for a Gamma(5) doublet ground state and a Gamma(3) singlet first excited state located at 15.6 K in the crystalline electric field scheme. The C-44 and C-66 of DyCu2Si2 also show softening below 70 K down to T-N1 = 9.7 K. A low-lying pseudo-sextet state consisting of three Kramers doublets of Gamma(6) circle plus 2 Gamma(7) brings about softening of C-44 and C-66 in DyCu2Si2.

DOI： 10.1088/0953-8984/25/29/296002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

The effect of pressure on the field-induced ordered phase for H aEuro- aOE (c) 111 > in the heavy-fermion compound YbCo2Zn20, which is presumably a field-induced antiferro-quadrupolar (FI-AFQ) phase, was investigated in the pressure range up to 4.5 GPa and under magnetic fields up to 80 kOe. When pressure is applied, the metamagnetic-like transition at H (m) =6 kOe shifts to lower fields and disappears around the quantum critical pressure P (c) similar to 1.8 GPa. A pressure-induced antiferromagnetic (PI-AFM) phase appears at pressures above about 2 GPa, and the critical field H (c) of the PI-AFM phase increases with increasing pressure. On the other hand, the transition field H (Q) of the FI-AFQ phase decreases gradually without showing any anomalous behavior around P (c) and becomes obscure around 4 GPa, where H (c) of the PI-AFM phase and H (Q) of the FI-AFQ phase become comparable. The magnetic field versus pressure, H-P, phase diagram for H aEuro- aOE (c) 111 > at 0.1 K was constructed in the pressure range up to 4.5 GPa.

DOI： 10.3938/jkps.62.1852

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

This report describes an outbreak of yersiniosis in Egyptian rousette bats (Rousettus aegyptiacus) caused by Yersinia pseudotuberculosis serotype 4b. Twelve of 61 bats died between November and December 2008 or in May 2009. The bats often displayed multiple yellow white nodules in the spleen and liver. Microscopically, these consisted of focal necrosis accompanied by inflammatory cell infiltration and colonies of gram-negative bacilli. The bacterial colonies were identified immunohistochemically as T. pseudotuberculosis 04 and T. pseudotuberculosis serotype 4b was identified by bacteriological examination. Polymerase chain reaction demonstrated that the isolate harboured the virulence genes virF,inv and ypmA. YPMa is as a superantigenic toxin that is associated with acute systemic infection in man and may contribute to the virulence of Y. pseudotuberculosis in bats. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jcpa.2012.07.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We carried out the de Haasvan Alphen (dHvA) experiment for an antiferromagnet UCd11 and its non-5f reference compound ThCd11 to clarify the Fermi surface properties and the true electronic specific-heat coefficient of UCd11. We observed dHvA signals of both compounds and compared the experimental results with the result of theoretical band calculations. The Fermi surfaces of both compounds are found to be small and closed. The cyclotron masses obtained from the dHvA data of UCd11 are compared with those of reference compounds ThCd11, NpCd11, and LaCd11, and the value of UCd11 is estimated to be about 100mJK2mol1, which is much smaller than the 840mJK2mol1 in the previous reports. It is concluded that this large value is mainly not due to heavy quasiparticles but due to the magnetic contribution to the specific heat.

DOI： 10.1002/pssb.201200765

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We present an overview of the Fermi-surface properties for antiferromagnets CeRh2Si2, CeIn3, CeRhIn5, and CeIrSi3, which were clarified from the de Haasvan Alphen (dHvA) experiments under strong magnetic fields up to 170kOe and high pressures up to 3GPa. A drastic change of the 4f-electronic state from a 4f-localized Fermi surface to a 4f-itinerant Fermi surface occurs in CeRh2Si2, CeIn3, and CeRhIn5 when the pressure P crosses a critical pressure Pc or P*c. Here, the Neel temperature TN disappears and the superconducting state appears at around Pc or P*c. A critical pressure P*c in CeRhIn5 is the pressure when TN is extrapolated to zero in the temperature vs. pressure phase diagram, and/or the antiferromagnetic state disappears completely even in magnetic fields. This is because the antiferromagnetic state is stable against magnetic fields, or in other words, the antiferromagnetic state recovers in magnetic fields. CeIrSi3 without inversion symmetry in the tetragonal structure is also similar to CeRhIn5 in the superconducting and Fermi-surface properties. It is characteristic that a huge upper critical field at zero temperature in superconductivity Hc2(0)similar or equal to 450 kOe is realized for H parallel to[001] in CeIrSi3 with the superconducting transition temperature Tsc=1.6K.

DOI： 10.1002/pssb.201200913

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We grew single crystals of an antiferromagnetic heavy-fermion compound UCd11 and a reference compound ThCd11, and carried out the magnetic susceptibility, high-field magnetization, and specific heat measurements in order to get more insight into the heavy fermion state which is realized in the antiferromagnetic state. The specific heat results suggest that the crystalline electric field (CEF) ground state of UCd11 is a doublet and the total splitting energy of the CEF scheme is less than 100 K. The H - T phase diagram for H parallel to < 100 > is approximately reproduced in the present experiments.

DOI： 10.1143/JPSJS.81SB.SB023

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

In the so-called 115 family members with chemical formulae of CeTIn5 (T=Co, Rh, Ir) and AnTGa(5) (An=U, Np, Pu), our analysis of the Knight shift and spin-lattice relaxation rates suggests that larger XY-type anisotropy in the antiferromagnetic spin fluctuations in the normal states would favor d-wave superconductivity with higher T-c. In order to examine this working hypothesis, the anisotropy ratios of antiferromagnetic fluctuations are derived from our NMR results for the superconductor NpPd5Al2 and antiferromagnet CePd5Al2, which are tetragonal compounds with a 115-related structure. CePd5Al2 shows Ising-type anisotropy, which is the same anisotropy as in the ordered state. On the other hand, NpPd5Al2 shows XY-type anisotropy just above T-c.

DOI： 10.1143/JPSJS.81SB.SB003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We measured the Hall coefficient in heavy fermion compounds YbT2Zn20 (T : Co, Rh, Ir) in the temperature range from 0.05 to 300 K. The Hall coefficient -R-H is found to indicate characteristic two extremals with a maximum and a minimum, reflecting a peak in the magnetic resistivity and the magnetic susceptibility.

DOI： 10.1143/JPSJS.81SB.SB062

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We present a magnetic torquemeter utilizing a piezoresistive microcantilever for use in pulsed high magnetic fields. Pulsed high magnetic fields are generated with a non-destructive pulsed magnet, which has a large bore diameter (48 mm) and a large sample space size (33 mm). Since differential gears are built into the sample space of this apparatus, it is possible to change sample angles against the magnetic field direction freely. By using this apparatus, we have performed the de Haas-van Alphen (dHvA) measurement on a high-quality Pb single crystal.

DOI： 10.1143/JPSJS.81SB.SB067

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We studied an effect of pressure on the heavy fermion state of YbCo2Zn20 under magnetic fields. The critical pressure P-c, where the electronic state changes from the heavy fermion state to the antiferromagnetic state, is estimated to be P-c similar or equal to 1.8 GPa. The super-heavy fermion state in the P-c region is found to be strongly destroyed in magnetic fields for H parallel to < 100 >. The field-induced quadrupolar phase, which is most likely realized only for H parallel to < 111 >, is found to be robust even in the antiferromagnetic pressure region.

DOI： 10.1143/JPSJS.81SB.SB064

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We succeeded in growing a single crystal of YbPd5Al2 with the tetragonal structure. The temperature dependence of electrical resistivity and a small value of the coefficient A in the Fermi liquid relation rho = rho(0) + AT(2) suggest that the 4f-electrons are well localized. A magnetic ordering was found at T-o = 0.19 K in the specific heat measurement. On the other hand, the magnetic entropy exhibits only 0.5R ln 2 at T-o, and the specific heat shows a long tail above T-o.

DOI： 10.1143/JPSJS.81SB.SB057

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Neel temperatures in RIr2Zn20 (R: rare earth) with the cubic caged structure are found to be very low, which are below T-N=5.0 K for GdIr2Zn20. This is mainly due to the long R-R distance and R atoms are spherically surrounded by Zn atoms. The corresponding crystalline electric field (CEF) splitting energies are also small, being below 100 K.

DOI： 10.1143/JPSJS.81SB.SB051

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We measured the de Haas-van Alphen oscillation in divalent compounds YbTIn5 (T : Co, Rh, Ir) and YbCoGa5. The Fermi surfaces, which are characteristic in two kinds of nearly cylindrical Fermi surface, are approximately unchanged in these compounds and are well explained by the results of energy band calculations. The cyclotron mass is found to increase remarkably as the average lattice constant decreases from 5.4 angstrom in YbIrIn5 to 5.2 angstrom in YbCoGa5: m(c)* = 1.1m(0) in YbIrIn5 and 5.1m(0) in YbCoGa5 for dHvA branch beta(1), revealing a chemical pressure effect. There exists the hybridization between 4f electrons and conduction electrons in YbCoGa5.

DOI： 10.1143/JPSJS.81SB.SB059

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We studied an effect of pressure on the electronic state of YbIr2Zn20 under magnetic fields. The heavy fermion state at ambient pressure is found to be changed into an antiferromagnetic state at pressures larger than a critical pressure P-c similar or equal to 5.2 GPa, where the electronic state indicates a super-heavy fermion state with an order of the electronic specific specific heat coefficient gamma = 20 J/(K-2.mol). The temperature dependence of the electrical resistivity shows a characteristic two-peak structure above 5.0 GPa, implying the combined phenomena between the Kondo effect and the crystalline electric field effect. At 7.6 GPa, the magnetoresistance shows a broad maximum at a critical field H-c, corresponding to a pressure-induced antiferromagnetic phase with the Neel temperature T-N = 1.4 K. T-N increases with further increasing pressure.

DOI： 10.1143/JPSJS.81SB.SB063

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

From the magnetization and magnetoresistance measurements, we constructed the magnetic phase diagram of Yb2Pt2Pb with the Shastry-Sutherland lattice, which consists of characteristic two phases below 1 K with many metamagnetic transitions, revealing magnetic frustrations.

DOI： 10.1143/JPSJS.81SB.SB058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The crystal structure of YbPdGe is orthorhombic, with a large lattice constant for the b-axis. Reflecting this crystal structure, the electronic state is well conductive in the a-c plane. Magnetically YbPdGe is a ferromagnet with a Curie temperature T-C = 11.4 K, and ferromagnetic moments are most likely oriented along the b-axis. The electronic specific heat coefficient gamma = 150 mJ/(K-2.mol) and a reduced magnetic entropy at T-C suggest that YbPdGe is a heavy fermion ferromagnet.

DOI： 10.1143/JPSJS.81SB.SB056

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

In order to get detailed insights into magnetism and its relationship with superconductivity, neutron scattering experiments were carried out on high-quality single crystals of the non-centrosymmetric heavy-fermion superconductor CePt3Si, with T-N=2.2 K and T-SC similar to 45 K. All the samples used in this study were characterised via specific heat measurements. Sharp specific heat jumps at T-sc=0.45 K, and T-N=2.2K for all samples prove the high quality of the crystal. The neutron diffraction study confirms that an antiferromagnetic peak described with the propagation vector q=(0 0 1/2) persists inside the superconducting state, with a tiny suppression of the magnetic intensity below T-sc. In contrast, an external magnetic field along the [0 0 1] direction causes a drastic change in the antiferromagnetic state; the antiferromagnetic intensity shows an enormous enhancement with increasing applied field. The magnetic intensity does not show any anomaly at B-c2, instead there exists a small inflection at around B' similar to 3.8 T where an additional phase boundary was reported. The huge increase in antiferromagnetic intensity corresponds to an increase of the staggered moment under uniform field, opposite of what is observed in ordinary antiferromagnets. These features suggest a weak coupling between magnetic and superconducting order parameters, and clearly evidence the anomalous antiferromagnetism in this compound.

DOI： 10.1143/JPSJS.81SB.SB006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We measured the electrical resistivity under magnetic field and pressure and de Haas van Alphen (dHvA) oscillations in CeCu6. The A value in the Fermi liquid relation of the electrical resistivity rho = rho 0 + AT(2) and the cyclotron effective mass are reduced with increasing magnetic fields and pressures. The A value, however, becomes distinct and/or is enhanced at the metamagnetic field, especially, in a characteristic pressure region where the electronic state deviates from the heavy fermion state, for example, at 2.00 GPa.

DOI： 10.1143/JPSJS.81SB.SB009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We report the superconducting properties of LaPt3Si poly and single crystals with non-centrosymmetric structure. We have measured ac magnetic susceptibility, chi(ac) - chi' + i chi'', under sweeping magnetic fields. On the chi', a peak ascribed to the differential paramagnetic effect DPE is observed just below critical fields, where the superconducting state of LaPt3Si collapses completely by an external magnetic field. However this DPE behavior disappears below 0.40 K. Additionally, in this temperature range, the width of the magnetic field of collapsing superconductivity becomes broader and the superconducting domains survive even in higher magnetic fields.

DOI： 10.1143/JPSJS.81SB.SB017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We measured the electrical resistivity, magnetic susceptibility, and specific heat in quasicrystal approximants RCd6. It was confirmed that the structural order-disorder transition of a tetrahedron with 4Cd atoms occurs at about 160 K when the lattice constant a is longer than a = 15.481 angstrom in YCd6, namely for RCd6 (R: Y, Pr, Nd, Sm, Gd, Tb, Dy and Yb). The structural transition is found to have a great influence on the low-temperature electrical resistivity.

DOI： 10.1143/JPSJS.81SB.SB019

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We report a pressure-induced evolution of magnetism and superconductivity in a helical magnet CeRhIn5 with an incommensurate wave vector Q(i) = (1\2, 1\2, 0.297) through the In-115 nuclear quadrupole resonance (NQR) measurements under P. From systematic measurements of the In-115-NQR spectrum, it is suggested that the commensurate antiferromagnetic order with Q(c) = (1\2, 1\2, 1\2) is realized near an antiferromagentic quantum critical point. The homogeneous coexistence of superconductivity and the commensurate antiferromagnetism is observed from the measurements of a nuclear spin-lattice relaxation rates (1/T-1) at 1.82 GPa. The analysis for 1/T-1 data below Tc indicates that the strong coupling superconductivity is realized above an antiferromagnetic quantum critical point.

DOI： 10.1143/JPSJS.81SB.SB013

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We succeeded in growing high-quality single crystals of V5Si3 with a high melting point of 2010 degrees C, and carried out the electrical resistivity, specific heat, magnetic susceptibility, and the de Haas-van Alphen measurements to clarify the electronic properties. The Fermi surface is small in volume and is well explained by the result of energy band calculations. The cyclotron mass is in the range from 5.3 to 0.2m(0) (m(0): rest mass of an electron), consistent with the electronic specific heat coefficient gamma = 9.7 mJ/(K-2.mol).

DOI： 10.1143/JPSJS.81SB.SB027

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We measured the electrical resistivity of a prototype heavy fermion antiferromagnet CeAl3 in the temperature range from 0.1 K to room temperature under various magnetic fields and pressures. The heavy fermion state at ambient pressure is drastically destroyed under a small pressure and magnetic field.

DOI： 10.1143/JPSJS.81SB.SB053

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Pressure driven valence fluctuations of a paramagnetic compound YbCu2Ge2, having the almost divalent configuration, has been investigated via the electrical resistivity (rho) measurement. Temperature dependence of the resistivity rho(T) shows typical metallic behavior expected for the non-magnetic metals at low pressure. With increasing pressure, the rho is strongly enhanced, and a broad shoulder-like anomaly appears in the rho(T) curve, as observed in the valence fluctuating system. The effective mass deduced from the rho(T) is strongly enhanced, indicating that YbCu2Ge2 changes to the heavy fermion system. The observation of the strong enhancement of the residual resistivity above 10 GPa, where the mass also starts to increase drastically, indicating the development of the valence fluctuation.

DOI： 10.1143/JPSJS.81SB.SB054

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The f electrons in rare earth and actinide compounds exhibit variety of characteristic properties including heavy fermions and unconventional superconductivity. Fermi surface properties in rare earth and actinide compounds such as CeSn3, USi3, NpGe3 and PuIn3 are clarified by the de Haas-van Alphen experiments on the basis of the results of energy band calculations. An abrupt nonlinear increase of magnetization, namely metamagnetic behavior is found in the heavy fermion compounds including YbT2Zn20 ( T: Co, Rh, Ir). An effect of pressure on the electronic state of YbIr2Zn20 and antiferromagnets CeRhIn5 and CeIrSi3 are also studied in magnetic fields. The electronic instability including unconventional superconductivity occurs at about 2.4 GPa in CeRhIn5 and 2.6 GPa in CeIrSi3.

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We succeeded in growing single crystals of LaNiC2 with the non-centrosymmetric orthorhombic structure by the Czochralski method, and measured the electrical resistivity, de Haas-van Alphen effect, and specific heat to clarify the Fermi surface and superconducting properties. This compound has been studied from a viewpoint of the triplet superconducting pairing state. In the present experiment, we observed an ellipsoidal Fermi surface and a multiply-connected-pillar Fermi surface, which are split into two Fermi surfaces, reflecting the antisymmetric spin-orbit interaction based on the non-centrosymmetric crystal structure. The two ellipsoidal Fermi surfaces are split by 230 K, for example. The anisotropy of electrical resistivity and upper critical field H-c2 in superconductivity are not large for three principal directions. From the low-temperature specific heat measurement, superconductivity in LaNiC2 is explained by the framework of the BCS-superconductivity, contrary to the above arguments. The upper critical field H-c2(0), which was obtained from the specific heat under magnetic fields, is about 2 kOe.

DOI： 10.1143/JPSJ.81.113703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report on a pressure-induced evolution of exotic superconductivity and spin correlations in CeIr(In1-xCdx)(5) by means of in-nuclear-quadrupole-resonance (NQR) studies. Measurements of an NQR spectrum and nuclear-spin-lattice-relaxation rate 1/T-1 have revealed that antiferromagnetism induced by Cd doping emerges locally around Cd dopants, but superconductivity is suddenly induced at T-c = 0.7 and 0.9 K at 2.34 and 2.75 GPa, respectively. The unique superconducting characteristics with a large fraction of the residual density of state at the Fermi level which increases with T-c differ from those for anisotropic superconductivity mediated by antiferromagnetic correlations. By incorporating the pressure dependence of the NQR frequency pointing to the valence change of Ce, we suggest that unconventional superconductivity in the CeIr(In1-xCdx)(5) system may be mediated by valence fluctuations.

DOI： 10.1103/PhysRevLett.109.117001

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Fermi surface properties in rare earth (R) and actinide (An) compounds of RX3 (X: Al, Ga, In, Si, Ge, Sn, Pb), AnX(3), RTIn5 (T: transition metal), and AnTGa(5) are clarified as a function of the number of valence electrons. The electronic state can be changed by applying pressure and magnetic field. A change of Fermi surface properties associated with the metamagnetic behavior and the quantum critical point is also clarified precisely, together with the split Fermi surfaces in the non-centrosymmetric crystal structure, and the de Haas-van Alphen oscillations in the superconducting mixed state. In the quantum critical point region, the conduction electrons, or quasi-particles, are of an f-electron character, with heavy effective masses of 10-100 m(0) (m(0) is the rest mass of an electron) and condense into the unconventional (anisotropic) superconducting state. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3683408]

DOI： 10.1063/1.3683408

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We measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat of the quasicrystal approximants RCd6 (R: rare earth, Y-Lu) with a body-centered cubic (bcc) crystal structure. Single crystals were grown by the Cd-self flux method and annealing method. We confirmed that the structural order-disorder transition is realized at about 160K when the lattice constant a is larger than 15.481 angstrom in YCd6, namely, for R = Pr, Nd, Sm, Gd, Tb, Dy, and Yb. At lower temperatures, RCd6 compounds, except non-4f reference compounds YCd6 and LuCd6, and a divalent compound YbCd6, are found to order antiferromagnetically. We clarified that the structural order-disorder transition has a great influence on the magnetic ordering and transport properties. The Neel temperature of RCd6 (R: Nd, Sm, Tb, and Dy) with the structural order-disorder transition is appreciably higher than the de Gennes scaling normalized by the Neel temperature of GdCd6, while the the Neel temperature of RCd6 (R: Ho, Er, and Tm) without the structural transition approximately follows the de Gennes scaling. Moreover, the electrical resistivity of RCd6 with the structural transition decreases monotonically below the Neel temperature, while it increases below the Neel temperature and a large residual resistivity remains at low temperatures in RCd6 without the structural transition. The contribution of an Einstein oscillator to the phonon specific heat is also discussed in YCd6 and LuCd6.

DOI： 10.1143/JPSJ.81.024720

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The metamagnetic behavior, which is typical in heavy fermion compounds, is observed in UCo2Zn20 and UIr2Zn20 at H-m = 80 and 20 kOe, respectively. Reflecting the metamagnetic behavior, the magnetoresistance is suppressed in magnetic fields larger than H-m, and the corresponding A-value of a Fermi liquid relation in the electrical resistivity sigma = sigma(0) + AT(2) indicates a peak at around H-m. Pressure suppresses this behavior in UIr2Zn20.

DOI： 10.1088/1742-6596/391/1/012021

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DC Magnetization of the heavy-fermion compound YbCo2Zn20 was examined at very-low temperatures down to 0.07 K in the field up to 14.5 T. In addition to the nearly-isotropic metamagnetic behavior at 0.6 T, a new metamagnetic behavior is observed in the field variation of magnetization M(H) at 6 T only for H parallel to [111]. For the same field direction, a clear kink appears in the temperature dependence of the magnetization M(T) for fields above 6 T. These results strongly suggest the existence of a new ordered phase induced by magnetic fields. The H - T phase diagram as well as the anisotropy in M(H) above similar to 2 T are best explained by a level crossing of the low-lying crystalline-electric-field states by magnetic fields.

DOI： 10.1088/1742-6596/391/1/012066

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We studied the magnetic field versus temperature phase diagram of the heavy-fermion compound YbCo2Zn20 with the cubic CeCr2Al20-type structure by measuring the specific heat, ac-susceptibility, and electrical resistivity under magnetic fields. In a low magnetic field region, a metamagnetic behavior was observed at H-m = 6 kOe for three principal field directions below T-chi max = 0.32 K, at which the temperature dependence of ac-susceptibility shows a local broad maximum. Two crossover lines were found below and above H-m. At high magnetic fields, the heavy-fermion state was rapidly suppressed with increasing magnetic field, and the field-induced ordered phase appeared in a very limited field direction around H parallel to < 111 > above the transition field H-Q = 60 kOe in the temperature range below T-Q = 0.6 K.

DOI： 10.1088/1742-6596/391/1/012072

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Inelastic neutron scattering experiments on poly crystalline sample of heavy-fermion compound YbCo2Zn20 were carried out in order to obtain microscopic insights on the ground state and its magnetic field response. At zero field at 300 mK, inelastic response consists of two features: quasielastic scattering and a sharp peak at 0.6 meV. With increasing temperature,a broad peak comes up around 2.1 meV, whereas quasielastic response gets broader and the peak at 0.6 meV becomes unclear. By applying magnetic field, the quasielastic response exhibits significant broadening above 1 T, and the peak at 0.6 meV is obscure under fields. The peaks in inelastic spectra and its temperature variation can be ascribed to the suggested crystal-field model of Gamma(6) - Gamma(8) - Gamma(7) with the overall splitting of less than 3 meV. The observed quasielastic response and its rapid broadening with magnetic field indicates that the heavy-electron state arises from the ground state doublets, and are strongly suppressed by external field in YbCo2Zn20,

DOI： 10.1088/1742-6596/391/1/012026

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We have measured the specific heat of poly- and single-crystalline LaPt3Si samples in various magnetic fields. In zero magnetic field, we observed distinct superconducting transitions at T-c similar to 0.64 K and 0.61 K for the poly- and single crystals, respectively. Temperature T dependences of the specific heat C of both samples around T-c resembled each other and could be well described by an exponential equation for a conventional superconductor at low temperatures. In a magnetic field, a characteristic peak of C/T appeared while the T-c was considerably suppressed. These trends were pronounced for the single crystal. The transition of the polycrystal became broad above 40 Oe and a characteristic tail appeared at temperatures above the peak of C/T. We suggest that the tail is induced by domains that have crystallographic disorders of the non-centrosymmetry and a higher critical magnetic field than that of the bulk. These domains became superconducting at temperatures above the peak of C/T, and then formed the tail. Both the poly- and single-crystalline LaPt3Si samples have been found to show characteristics that are in-between those of type-I and type-II superconductors.

DOI： 10.1088/1742-6596/400/2/022079

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We have carried out the electrical resistivity measurements under high pressures up to 24 GPa for CeTX3 (T: Co and Ir, X: Si and Ge), CePd5Al2 and YbIr2Zn20 in order to investigate quantum criticality and superconductivity. Antiferromagnets CeTX3 with the non-centrosymmetric tetragonal structure show superconductivity under high pressures and reveal a huge upper critical field for H parallel to [001]. An antiferromagnet CePd5Al2, which is an isostructural family of a heavy fermion superconductor NpPd5Al2, also shows superconductivity under high pressures. In these compounds, superconductivity appears in the vicinity of quantum critical point. On the other hand, YbIr2Zn20 without magnetic ordering approaches to the quantum critical point with increasing pressure, and exhibits a super-heavy fermion state exceeding 10 J/(K-2 center dot mol).

DOI： 10.1088/1742-6596/400/2/022028

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The property of Fermi surface splitting in the non-centrosymmetric tetragonal compounds RPt 3Si (R: La, Ce) and RT X 3 (T: Co, Rh, Ir
X: Si, Ge) are studied by de Haas-van Alphen experiments and compared with energy band calculations. Moreover superconducting properties are investigated in these compounds. In particular, in CeIrSi 3 the unusual behavior of the upper critical field H c2 at pressures around 2.6 GPa is analyzed in detail. At 2.6 GPa, a huge value of H c2(0) ≃450 kOe is found for magnetic fields along the [0 0 1] direction of the non-centrosymmetric tetragonal crystal structure, in contrast to the smaller H c2(0) ≃ 95 kOe for H ∥ [1 1 0]. © Springer-Verlag Berlin Heidelberg 2012.

DOI： 10.1007/978-3-642-24624-1_3

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Language：English   Publisher：The Surface Science Society of Japan  

Systematic study of the 4f electronic state in RRhIn 5 and RCu 2Si 2 has been done by using single crystalline samples which were successfully grown by the flux method. Most of RRhIn5 compounds order antiferromagnetically at low temperatures, except when R=Y, La, Pr and Yb. The observed anisotropic features in the magnetic susceptibility and magnetization have been analyzed on the basis of the crystalline electric field (CEF) model. The observed anisotropy in the magnetic susceptibility in the paramagnetic state is well explained by the CEF effect. Specific heat measurements on a series of ternary compound RCu 2Si 2 have been performed by the quasiadiabatic heat pulse method in the temperature range down to 100 mK. We observed the nuclear specific heat at low temperatures and estimated the magnitude of internal effective magnetic field H eff at the nucleus in RCu 2Si 2. © 2011 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2011.446

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Pressure and temperature dependences of the electronic structure of the heavy-fermion superconductor CeIrSi3 have been investigated using partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Ce L-3 edge. Ce is in a weakly mixed valence state at ambient pressure, mostly f(1) with a small contribution from the f(0) component. Pressure-induced increase of the Ce valence becomes apparent above 4 GPa, concomitantly with the disappearance of the superconductivity. No temperature dependence of the Ce valence is observed within the measured temperature range down to 24 K.

DOI： 10.1143/JPSJ.80.124701

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We have measured three-dimensional band structure and Fermi surfaces (FSs) ofYbCu(2)Ge(2), which has recently become recognized as a nearly divalent Yb-based compound, by using soft x-ray angle-resolved photoemission spectroscopy. We clarified that the bands with finite Yb 4f contribution cross the Fermi level and are slightly involved in the formation of the FSs, in line with the valence-fluctuating state of YbCu2Ge2. The obtained valence-band dispersions and the FSs are well explained by a relativistic band-structure calculation based on a local-density-approximation (LDA). These results suggest that the LDA calculation is a good starting point for understanding of the electronic state of YbCu2Ge2 as well as nearly divalent Yb-based compounds.

DOI： 10.1103/PhysRevB.84.195121

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Magnetic susceptibility, high-field magnetization up to 500 kOe, and specific heat in a wide temperature range from 0.06 to 300K were measured for single crystals of the cubic heavy-fermion compound YbCo2Zn20 in order to elucidate the electronic states of the compound at low temperatures. A strong increase in the magnetic specific heat in the form of C-mag/T below similar to 1K is approximately explained by the resonant level model for S = 1/2 with the Kondo temperature T-K = 1 K, and an extremely large C-mag/T similar or equal to 8 J/(K-2.mol) below about 0.2K is explained by considering the magnetic entropy of the doublet ground state in the 4f crystalline electric field (CEF) scheme of an Yb3+ ion, which corresponds to an extremely large electronic specific heat coefficient. The field-induced ordered phase for H parallel to < 111 >, which has recently been found by low-temperature magnetization measurements, was precisely studied by electrical resistivity and specific heat measurements, and was observed in a limited angular range around the < 111 > direction. On the basis of CEF analyses, the level crossing of the two lowest CEF states is essentially important to understand the field-induced ordered phase, which can be reduced to a field-induced antiferro-quadrupolar ordering based on the Gamma(3)-type quadrupole moment O-2(0).

DOI： 10.1143/JPSJ.80.114703

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We have carried out the electrical resistivity and ac specific heat measurements under pressure P and magnetic field H in a pressure-induced superconductor CeIrSi3 with the noncentrosymmetric tetragonal crystal structure. Superconductivity is observed in a wide pressure region from 1.9 GPa to about 3.5 GPa. The antiferromagnetic state disappears at P-c = 2.25 GPa under H = 0, but in magnetic field we have found an antiferromagnetic state. The corresponding electrical resistivity in constant magnetic field decreases rather steeply below the Neel temperature T-N under pressures up to about 2.4 GPa, while it shows an upturn anomaly at T-N under pressures larger than 2.4 GPa. The ac specific heat also indicates a clear jump at T-N in magnetic field. When the antiferromagnetic phase exists in magnetic field, the superconducting transition becomes broad, possessing a transition width Delta T-sc = 0.2-0.5 K. On the other hand, it becomes extremely sharp, with Delta T-sc = 0.03K even at 17 T under P = 2.55 GPa, for example, when the antiferromagnetic phase disappears. The upper critical field H-c2 for H parallel to [001] is also extremely enhanced around 2.5-2.7 GPa, and the H-c2(0) value reaches about 45 T at P-c* similar or equal to 2.63 GPa, even though the superconducting transition temperature T-sc = 1.6K is very small. The electronic instability is realized in magnetic field at P-c*. The present characteristic heavy fermion superconductivity in the noncentrosymmetric structure is compared with the similar pressure-induced superconductivity of CeRhIn5.

DOI： 10.1143/JPSJ.80.094703

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We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in LaRu2Al10, which is a reference compound of CeRu2Al10 that exhibits an unusual transition at T-0 similar or equal to 27 K. The magnetoresistance increases with increasing magnetic field at low temperatures in the wide field directions, suggesting that LaRu2Al10 is a compensated metal without an open orbit. From the dHvA experiments, about three dHvA frequency branches whose cyclotron effective masses are close to 1m(0) (m(0): rest mass of an electron) were detected. The observed dHvA branches for the main Fermi surface are well explained by the results of band structure calculation based on a full potential linearized augmented-plane-wave (FLAPW) method and local-density approximation (LDA), that demonstrates the multiply connected Fermi surface with no nesting property in LaRu2Al10.

DOI： 10.1143/JPSJ.80.084716

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Strain and resistivity measurements in UIr showed the occurrence of two structural phase transitions under high pressure, indicating the existence of three phases I-III, with slightly different crystal structures. It is suggested that ferromagnetic phases FM1-FM3 emerge in phases I-III, respectively. The pressure-temperature phase diagram was sensitive to the hydrostaticity of pressure. FM3 and superconductivity are observed in the measurements in which Daphne 7373 is used as a pressure-transmitting medium; however they are both absent in the case where petroleum ether is used as a pressure-transmitting medium. These results indicate a close relationship between ferromagnetism and superconductivity.

DOI： 10.1103/PhysRevB.84.054524

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We studied the Fermi surface properties of YbCu2Si2 and YbCu2Ge2 with the tetragonal structure by measuring the de Haas-van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4f electrons contribute to the Fermi surface of a valence fluctuating compound YbCu2Si2, but not to that of a divalent compound YbCu2Ge2. Namely, the Fermi surface of YbCu2Si2 contains the 4f-components considerably and the corresponding cyclotron effective mass m(c)* of the main Fermi surface is large, m(c)*=30-40m(0) (m(0) : rest mass of an electron). We also studied the heavy fermion properties of YbT2Zn20 (T : Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed at 6 kOe in YbCo2Zn20, 63 kOe in YbRh2Zn20, and 97 kOe in YbIr2Zn20 for H parallel to < 100 >, which was measured at 60 mK in YbCo2Zn20 and 1.3 K in YbRh2Zn20 and YbIr2Zn20. The metamagnetic field is found to be a good parameter to reach the quantum critical point under pressure for YbIr2Zn20. By measuring the electrical resistivity under pressure and magnetic field, we clarified that the electronic state close to the quantum critical point is realized in YbIr2Zn20 at 5.2 GPa and also YbCo2Zn20 at ambient pressure. The corresponding heavy cyclotron effective mass of 100-500m(0) at 0 kOe was estimated from the field dependence of the root A value in the low-temperature electrical resistivity rho = rho(0) + AT(2) under pressure and magnetic field and the cyclotron mass obtained from the dHvA experiment at ambient pressure and high magnetic fields.

DOI： 10.1143/JPSJS.80SA.SA003

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We report on de Haas-van Alphen effect measurements in the non-centrosymmetric systems CeCoGe3 and LaCoGe3 in magnetic field up to 28 Testa. In both compounds, two new high frequencies were observed in high fields. The frequencies were not detected in previous lower field measurements. The frequencies do not originate from magnetic breakdown, and, therefore, are likely to be intrinsic features of the compounds. In CeCoGe3, the corresponding effective masses are strongly enhanced, being of the order of 30 bare electron masses.

DOI： 10.1143/JPSJS.80SA.SA020

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We have measured the electrical resistivity under magnetic field and pressure for YbIr2Zn20 with the cubic caged structure, and created the evolution of an electronic state in the quantum critical region. The new electronic state at about 5.0 GPa corresponds to the heavy ferrmion state with a very small Kondo temperature T-K = 0.1 - 0.2 K from the metamagnetic behavior observed at the magnetic field H-m = 1.5 kOe. The corresponding cyclotron effective mass at 0 kOe is estimated to be about 450 m(0).

DOI： 10.1143/JPSJS.80SA.SA050

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DC magnetization of YbIr2Zn20 was measured in magnetic fields H (parallel to [100]) up to 14.5 T at low temperatures down to 0.09 K, focusing attention on the metamagnetic behavior. At the base temperature of T = 0.09 K, three sharp structures were observed in the differential susceptibility dM/dH at 6.2, 9.7 and 11.2 T, with the peak at 9.7 T being the largest. The amplitudes of these anomalies are strongly T dependent and those at 6.2 and 11.2 T disappear above 0.7 and 0.4 K, respectively. The peak value of dM/dH of the main peak at 9.7 T exhibits an unusual temperature variation on cooling below 1 K, with a divergent tendency persisting towards the lowest temperature. This feature is different from what one would expect for the normal Fermi liquid systems, and suggests the existence of underlying quantum critical behavior. The results are discussed in relation to the recently proposed field-induced valence crossover scenario.

DOI： 10.1143/JPSJS.80SA.SA051

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The metamagnetic behaviour, which corresponds to one of the characteristic properties in the heavy fermion compounds, was studied by measuring the electrical resistivity under pressure and magnetic field for a typical heavy fermion compound CeCu6 with orthorhombic structure. The transverse magnetoresistance at 100 mK indicated a peak structure at H-m = 20 kOe for the magnetic field H//c-axis under ambient pressure. H-m is found to increase linearly as a function of pressure and indicates H-m = 102 kOe at 1.75 GPa, for example. The quantum critical point is thus likely to exist at a slightly negative pressure value of similar to 0.21 GPa from extrapolating H-m to zero. The rho(0) and A values in the electrical resistivity rho = rho(0) + AT(2) decrease steeply in magnitude with increasing pressure and magnetic field, indicating that the heavy fermion state is destroyed by pressure and magnetic field.

DOI： 10.1143/JPSJS.80SA.SA065

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We measured electrical resistivity on antiferromagnet Ce2Ir3Ge5 under high pressure up to 8 GPa. It is shown that the Neel temperature (= 9.5 K) at ambient pressure decreased by increased pressure. The Neel temperature seems to be zero at a critical pressure P-c similar or equal to 2.0 GPa suddenly. The variation by higher pressure above 2.0 GPa does not seem prominence up to 8 GPa.

DOI： 10.1143/JPSJS.80SA.SA066

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We have measured specific heat of poly and single crystalline LaPt3Si samples under various magnetic fields. For zero magnetic field, we observed a distinct peak and jump in the specific heat at the super-conducting transition temperature T-c similar to 0.64 K and 0.61 K for the poly and single crystals, respectively. Temperature dependences of the specific heat of both samples below T-c can be well-described by a exponential equation for a conventional superconductor at zero magnetic field. The jump at T-c of single crystal is still distinct under magnetic fields. On the other hand, the peak of the poly crystal becomes broad above 40 Gauss. The broad additional specific heat tail appears at higher temperatures than the T-c expected from the results of the single crystal. We show, for the first time, the temperature dependence of superconducting critical magnetic field H-c(T) obtained from the specific heat measurement. Small anisotropy of H-c(T) was observed for the single crystal, with H-c,(0) = 66 and 61 Gauss for H//a and H//c, respectively.

DOI： 10.1143/JPSJS.80SA.SA070

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CeIrSi3 is an antiferromagnet with a Neel temperature T-N=5.0 K at ambient pressure. With increasing pressure, T-N decreases monotonically and the antiferromagnetic (AF) ordering disappears at pressure P-c=2.25 GPa, and shows pressure-induced superconductivity above 1.9 GPa. We have investigated the superconducting and field-induced AF states in CeIrSi3 by measureing the electrical resistivity and ac-specific heat measurements under pressure and magnetic field. At 2.40 GPa, for example, the AF phase is induced by magnetic field above 6 T. The upper critical field H-c2 is suppressed in the field-induced anti-ferromagneic phase. We discussed the field-induced AF state in CeIrSi3, comparing with that in CeRhIn5, which possesses a similar pressure phase diagram.

DOI： 10.1143/JPSJS.80SA.SA069

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We have fabricated a 3-axes magnetometer that can reduce the residual magnetic field below 50 mu G for each direction. Josephson critical current I-c between a noncentrosymmetric superconductor (CePt3Si or LaPt3Si) and Al has been investigated inside it to avoid the magnetic-flux trapping during the superconducting transition and found to show a magnetic field H dependence similar to the previous one obtained using one-axis magnetometer; asymmetric patterns with respect to H = 0 are commonly observed for CePt3Si and LaPt3Si. This suggests that the residual-field components perpendicular to H applied for I-c(H) measurements does not basically affect the I-c(H) patterns.

DOI： 10.1143/JPSJS.80SA.SA071

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beta-US2 with the orthorhombic structure is an interesting compound of which the electrical property is changed from a metallic state to an insulating state at temperatures lower than 80 K. To clarify the present metal-insulator change, we carried out the magnetization and magnetoresistance measurements in magnetic fields up to 50 T. The magentization at 4.2 K saturates above 40 T, reaching 1.75 mu(B)/U at 50 T for the magnetic field along the magentic easy-axis, namely the [001] direction. The corresponding electrical resistivity at 4.2 K is steeply reduced in magnitude from 1 x 10(3) Omega.cm to 2 x 10(-2) Omega.cm at 50 T only when the magnetic field is applied along the [001] direction. The temperature dependence of the electrical resistivity at 50 T indicates a usual metallic behaviour. The conduction electrons are most likely released from the trapped U-sites when the 5f-CEF magnetic moments are fully polarized in high magnetic field of 50 T. The present experimental results are discussed from the viewpoint of the magnetic polaron.

DOI： 10.1143/JPSJS.80SA.SA104

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DC magnetization (M) measurements were done on a single crystal of YbCo2Zn20 at very low temperatures (T) down to 0.07 K in magnetic fields H parallel to [111]. In addition to the metamagnetic behavior at mu H-0(m) = 0.6 T already known, we found a new metamagnetic transition at mu H-0'(m) = 6 T whose critical field moves to higher fields with increasing T. Moreover, in fields above 6 T, temperature dependence of the magnetization M(T) shows a kink below 0.6 K. These anomalies indicate the presence of a new field-induced ordered phase. In addition, a broad peak is observed in M(T) in fields above 3 T outside the ordered phase. These results are best explained by a level crossing of the low-lying crystalline-electric-field state with the ground state, possibly assisted by a valence change in magnetic fields.

DOI： 10.1143/JPSJ.80.073707

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We measured the de Haas-van Alphen (dHvA) oscillations, electrical resistivity, magnetic susceptibility, magnetization, and specific heat of PrIr2Zn20, which has recently been suggested as a heavy-fermion superconductor. Several dHvA branches with small frequencies ranging from 0.33 x 10(6) to 8.00 x 10(6) Oe were detected in the dHvA experiment, which were well explained by the results of energy band calculations for LaIr2Zn20 using the lattice parameter of PrIr2Zn20. Moreover, the cyclotron effective mass is small, i.e., less than 1m(0) (m(0): rest mass of an electron). This means that 4f electrons are fully localized and do not contribute to the Fermi surface. Similar dHvA results were obtained for the reference compound LuIr2Zn20. Thus, superconductivity in PrIr2Zn20, which has been observed very recently below 0.05 K, is not due to heavy quasiparticles. In fact, the present superconductivity disappears at a magnetic field of 20 Oe. From the experimental results of magnetic susceptibility, magnetization, and specific heat, we estimated the 4f crystalline electric field (CEF) scheme of PrIr2Zn20: Gamma(3) (0 K)-Gamma(4) (separated from a non-Kramers Gamma(3) doublet by 36.0 K)-Gamma(1) (86.4 K)-Gamma(5) (103 K). On the basis of this CEF scheme, we discuss a broad Schottky peak in the magnetic specific heat at 0.4K and the metamagnetic-like anomaly of magnetization at H-m similar or equal to 50 kOe for H parallel to < 100 >.

DOI： 10.1143/JPSJ.80.074605

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We studied the electronic state and metamagnetic behavior in the heavy fermion compound YbCo2Zn20 by measuring the specific heat, ac-susceptibility, and electrical resistivity under magnetic fields. The magnetic specific heat in the form of C-mag/T increases steeply with decreasing temperature below 10 K and becomes constant with an extremely large value 8 J/(K-2.mol) below about 0.2 K, indicating a Fermi-liquid nature in this temperature range. The magnetic entropy increases rapidly below 10 K and reaches R ln 8 around 60 K, suggesting a small crystalline-electric-field (CEF) splitting energy. From the precise electrical resistivity measurements, together with the C(H)/T and chi(ac) (T) measurements, it was found that there are two crossover lines at low temperatures in the H-T phase diagram for H parallel to < 100 >. The Fermi-liquid state evolves at lower temperatures than these crossover lines.

DOI： 10.1143/JPSJS.80SA.SA052

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We have investigated the electronic structures of Rh17S15 by using soft x-ray photoemission spectroscopy and first principle band structure calculations. While S 2p core level spectra are explained by symmetric components, Rh 3d core level exhibits asymmetric line shape, suggesting a dominant Rh 4d character at the states near the Fermi level. The binding energy of Rh 4d in Rh17S15 is similar to the one in Rh metal, and this observation implies metallic Rh-Rh bonding. Many features in experimental valence spectra are reasonably described by the calculations, indicating that one particle approximation is a good starting point to understand the electronic properties of Rh17S15. The comparison between the experiment and the calculation suggests that Rh 4d character at the states near the Fermi level is essential for the correlated superconductivity in Rh17S15. However, some deviation between the experiment and the calculation as well as a finite mass enhancement are found, indicating some corrections on the treatment of electron-phonon coupling and/or electron correlations are necessary.

DOI： 10.1143/JPSJS.80SA.SA111

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DOI： 10.1143/JPSJ.80.065001

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Resistivity measurements performed under pressure in the paramagnetic ground state of CeRu2Si2 are reported. They demonstrate that the relative change of effective mass through the pseudo metamagnetic transition is invariant under pressure. The results are compared with the first order metamagnetic transition due to the antiferromagnetism of Ce0.9La0.1Ru2Si2 which corresponds to the "negative" pressure of CeRu2Si2 by volume expansion. Finally, we describe the link between the spin-depairing of quasiparticles on CeRu2Si2 and that of Cooper pairs on the unconventional heavy fermion superconductor CeCoIn5.

DOI： 10.1143/JPSJ.80.053702

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We succeeded in growing high-quality single crystals of a heavy electron compound. YbCu2Si2. The electronic specific beat coefficient gamma is determined to be 150 mJ/K-2.mol, which is consistent with, the A lie; of the electrical resistivity from Kadowaki-Woods relation. We succeeded in observing the de Haas-van Alphen (dHvA) oscillations. The dHvA frequencies and large cyclotron effective masses in YbCu2Si2 are highly different from those in a non-4f reference compound YCu2Si2. From these dHvA results, the heavy electron state of YbCu2Si2 is characterized by the large contribution of 4f-electrons to the topology of the Fermi surface and also to the strong enhancement of effective mass caused by the spin fluctuations. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200983027

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Antiferromagnets CePd5Al2 and CeRhGe2 with the quasi-two dimensional electronic state have been found to become superconductive by measuring the electrical resistivity under pressure. In these compounds, the Neel temperature decreases at high pressure and becomes approximately zero at critical pressure P-c = 9 GPa in CePd5Al2 and P-c = 7 GPa in CeRhGe2. Superconductivity was observed around P-c. In CePd5Al2, the upper critical field H-c2 is found to be highly anisotropic among H parallel to [001] and [100], reflecting nearly cylindrical Fermi surfaces along the tetragonal [001] direction. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200983055

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We succeeded in growing sin-le crystals of the antiferromagnet CePd5Al2, and the paramagnet PrPd5Al2 with a tetragonal crystal structure by the Bridgman method, and studied the magnetic and surface properties by measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat, and de Haas-van Alphen (dHvA) oscillation. We constructed the crystalline electric field (CEF) scheme from the experimentally observed anisotropic magnetic Susceptibility and magnetization Of CePd5Al2 and PrPd5Al2. In both compounds, the B-2(0) Value in the CEF parameters is negative and large, implying that the magnetic easy axis is the [001] direction. The present magnetism of CePd5Al2 and PrPd5Al2 is highly different from that of the heavy fermion superconductor NpPd5Al2 with the magnetic easy axis of the [100] direction. From the dHvA experiment for CePd5Al2 and PrPd5Al2, we observed a few dHvA branches. which correspond to nearly cylindrical band-32 hole and band-33 electron Fermi surfaces Of the non-4f reference LaPd5Al2, Reflecting the anisotropy of effective masses based on the nearly cylindrical Fermi surfaces along the tetragonal [001] direction, the Upper critical field H-c2 for H parallel to [100] in the pressure-induced superconductor CePd5Al2], is larger than that for H parallel to [001]: -dH(c2)/dT = 100kOe/K for H parallel to [100], and -dH(c2)/dT = 18kOe/K for H parallel to [001] at the superconducting transition temperature T-sc = 0.9 K. This anisotropy in H-c2 is also highly different from that of NpPd5Al2, suggesting that superconductivity is closely correlated with magnetism.

DOI： 10.1143/JPSJ.79.024702

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Using the de Haas-van Alphen effect we have measured the evolution of the Fermi surface of BaFe2(As1-xPx)(2) as a function of isoelectric substitution (As/P) for 0.41 < x < 1 (T-c up to 25 K). We find that the volumes of electron and hole Fermi surfaces shrink linearly with decreasing x. This shrinking is accompanied by a strong increase in the quasiparticle effective mass as x is tuned toward the maximum Tc. These results are not explained by simple band structure calculations, and it is likely that these trends originate from the same many-body interactions which give rise to superconductivity.

DOI： 10.1103/PhysRevLett.104.057008

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To identify the superconducting gap symmetry in CeCoIn5 (T-c = 2.3 K), we measured the angle-resolved specific heat (C-phi) in a field rotated around the c axis down to a very low temperature, 0.05T(c), and made detailed theoretical calculations. In a field of 1 T, a sign reversal of the fourfold angular oscillation in C-phi was observed at T similar or equal to 0.1T(c) upon entering a quasiclassical regime where the maximum of C-phi corresponds to the antinodal direction, coinciding with the angle-resolved density of states (ADOS) calculation. The C-phi behavior, which exhibits minima along the [110] directions, unambiguously allows us to conclude d(x2-y2) symmetry of this system. The ADOS-quasiclassical region is confined to a narrow T and H domain within T/T-c similar to 0.1 and 1.5 T (0.13H(c2)).

DOI： 10.1103/PhysRevLett.104.037002

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We report Si-29 NMR study on a single crystal of the heavy-fermion superconductor CeIrSi3 without an inversion symmetry along the c axis. The Si-29 Knight-shift measurements under pressure have revealed that the spin susceptibility for the ab plane decreases slightly below T-c, whereas along the c axis it does not change at all. The result can be accounted for by the spin susceptibility in the superconducting state being dominated by the strong antisymmetric (Rashba-type) spin-orbit interaction that originates from the absence of an inversion center along the c axis and it being much larger than superconducting condensation energy. This is the first observation which exhibits an anisotropy of the spin susceptibility below T-c in the noncentrosymmetric superconductor dominated by strong Rashba-type spin-orbit interaction.

DOI： 10.1103/PhysRevLett.104.017002

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We report the results of Pd-105 NQR experiments on NpPd5Al2 and CePd5Al2. In the normal state at 6 K, the Pd-105 NQR spectrum consists of four lines in both systems. These lines can be assigned to two sets of +/- 1/ 2 <-> +/- 3/2 and +/- 3/2 <-> +/- 5/2 NQR transitions arising from two crystallographically inequivalent Pd sites. From the analysis of the Pd-105 NQR spectrum the nuclear quadrupole frequency nu(Q), asymmetry parameter eta and electric field gradient V-zz have been deduced.

DOI： 10.1088/1742-6596/200/1/012020

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We studied the electronic states of three typical neptunium compounds, NpGe3, NpRhGa5 and NpCd11. Among them, NpGe3 and NpCd11 with the cubic crystal structure are paramagnets without magnetic ordering, while NpRhGa5 with the tetragonal structure is an antiferromagnet. At high temperatures, the 5f electrons in NpGe3 are almost localized, and the magnetic susceptibility chi(T) approximately follows the Curie-Weiss law. With decreasing temperature, chi(T) shows a broad peak around 50 K, indicating a moderate heavy fermion state at lower temperatures. In fact, the results of the de Haas-van Alphen (dHvA) experiments for NpGe3 are well explained by the 5f-itinerant band model; namely, the 5f electrons contribute to the Fermi surface and the cyclotron effective mass. The cyclotron mass is thus enhanced, ranging from 2.6 to 16 times the rest mass of the electron m(0). In the antiferromagnet NpRhGa5, it was clarified from the results of dHvA experiments and energy band calculations that the 5f electrons contribute to the Fermi surface. The cyclotron mass varies from 8.1 to 11.7 m(0), and the magnetic moment is 0.89 mu(B)/Np. In NpCd11, the 5f electrons are localized in the whole temperature range and do not contribute to the Fermi surface. The corresponding cyclotron mass is thus light, below 1 m(0), revealing no hybridization between the localized 5f electrons and the conduction electrons. The Fermi surface consists of small closed Fermi surfaces, reflecting the small Brillouin zone associated to the large unit cell of the crystal structure in NpCd11. The long Np-Np nearest-neighbor distance (6.568 angstrom) results in the well localized 5f(4) states. Magnetic susceptibility and magnetization curves are well explained in a crystalline electric field (CEF) scheme assuming a singlet ground state and an excited triplet state separated by a 120 K energy gap.

DOI： 10.1088/1757-899X/9/1/012089

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We report muon Knight shift measurements in single crystals of CeCoIn5 below 17 kOe. The muon Knight shift decreases with decreasing temperature below T-c and the reduction of the Knight shift is roughly explained by the Fermi liquid relation. The magnetic field dependence of the reduction of the muon Knight shift is not in proportion to root H. This fact is inconsistent with simple expectation for a d-wave superconductor.

DOI： 10.1088/1742-6596/225/1/012013

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We report the superconducting characters in CeIrIn(5) studied by In-NQR measurements under pressure (P). In CeCoIn(5) and CeRhIn(5), the occurrence of superconductivity (SC) is related with the antiferrmagnetic spin fluctuations (AFM-SFs) originating from the antiferromagntic quantum-critical point (AFM-QCP). The high-T(c) SC (T(cmax) > 2 K) is realized in both compounds. However, in CeIrIn5 which is apart from the AFM-QCP, SC occurs even without AFM-SFs and the quite small value of T(cmax) (similar to 1 K) is observed around P = 3 GPa. The mechanism of SC in CeIrIn(5) may be different from that in CeCoIn(5) and CeRhIn(5).

DOI： 10.1088/1742-6596/200/1/012087

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We present a phase diagram for the antiferromagnetism and superconductivity in Ce(2)RhIn(8) probed by In-NQR studies under pressure (P). The quasi-2D character of antiferromagnetic spin fluctuations in the paramagnetic state at P = 0 evolves into a 3D character because of the suppression of antiferromagnetic order for P > P(QCP) similar to 1.36 GPa (QCP: antiferromagnetic quantum critical point). Nuclear-spin-lattice-relaxation rate 1/T(1) measurements revealed that the superconducting order occurs in the P range 1.36 - 1.84 GPa, with maximum T(c) similar to 0.9 K (P(QCP) similar to 1.36 GPa).

DOI： 10.1088/1742-6596/200/1/012238

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Since the discovery of a heavy fermion superconductor CeCu2Si2 in 1979, heavy fermion superconductivity has been observed in several rare earth and actinide compounds. Especially the development of high pressure technique and crystal growth makes it possible to investigate the pressure-induced superconductivity in the heavy fermion compounds, possessing magnetic ordering at ambient pressure. In this article, we present recent advances in pressure-induced superconductivity around antiferromagnetic fluctuation, focusing on CeRhIn5 and CeIrSi3.

DOI： 10.4131/jshpreview.20.124

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We grew single crystals of RCoGe3 (R: La, Cc, Pr, and Nd) by the Bi-flux method, and studied the magnetic properties of PrCoGe3 and NdCoGe3 and the pressure-induced superconducting property of CeCoGe3. These compounds crystallize in a non-centrosymmetric tetragonal structure. PrCoGe3 and NdCoGe3 were found to be a paramagnet and an anti ferromagnet with the Neel temperature T-N = 3.8 K, respectively. Crystalline electric field (CEF) schemes were proposed for PrCoGe3 and NdCoGe3. The magnetic property of a pressure-induced superconductor CeCoGe3 is highly different from those of PrCoGe3 and NdCoGe3, or a similar pressure-induced superconductor CeIrSi3. This was discussed in connection with the superconductivity of CeCoGe3. We clarified the upper critical field H-c2 for H parallel to [001] and [100] by measuring the electrical resistivity under pressure P in magnetic fields: H-c2(0) similar or equal to 24T for H parallel to [001] and H-c2(0) similar or equal to 3.1 T for H parallel to [100] at 0 K at P = 7.1 GPa. A huge H-c2(0) value for H parallel to [001] is a combined phenomenon between the Rashba-type antisymmetric spin-orbit interaction and the electronic instability, as observed in CeIrSi3.

DOI： 10.1143/JPSJ.78.124713

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We measured the high-field magnetization and de Haas-van Alphen (dHvA) oscillations for YbIr2Zn20 with a cubic crystal structure, together with the electrical resistivity and magnetic susceptibility. The magnetic Susceptibility chi with an effective magnetic moment of Yb3+ becomes temperature-independent at low temperatures, with a broad peak at T-chi max = 7.4 K for H parallel to < 110 >. The corresponding magnetization indicates a metamagnetic transition at H-m = 120kOe, consistent with a T-chi max vs H-m relation in the Ce- and U-based heavy fermion Compounds. The large cyclotron masses of 4-27 m(0) are detected in the dHvA experiment, and are found to be reduced at magnetic fields higher than H-m = 120 kOe. The resistivity follows the Fermi liquid relation rho = rho(0) +AT(2) under magnetic field, and the root A value is also found to have a maximum at H-m as a function of magnetic field. From the present experimental results, together with the results of 4f-itinerant energy band calculations, the 4f electrons are found to contribute to the heavy fermion state in YbIr2Zn20.

DOI： 10.1143/JPSJ.78.123711

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We present a phase diagram for the antiferromagnetism and superconductivity in Ce2 RhIn8 probed by In-NQR studies under pressure (P). The quasi-two-dimensional character of antiferromagnetic spin fluctuations in the paramagnetic state at P=0 evolves into a three-dimensional character because of the suppression of antiferromagnetic order for P&gt
PQCP ∼1.36GPa (QCP: quantum critical point). Nuclear-spin-lattice relaxation rate 1/ T1 measurements revealed that the superconducting order occurs in the P range 1.36-1.84 GPa, with maximum Tc ∼0.9K around PQCP ∼1.36GPa. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.80.184503

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We present a phase diagram for the antiferromagnetism and superconductivity in Ce2RhIn8 probed by In-NQR studies under pressure (P). The quasi-two-dimensional character of antiferromagnetic spin fluctuations in the paramagnetic state at P=0 evolves into a three-dimensional character because of the suppression of antiferromagnetic order for P>P-QCP similar to 1.36 GPa (QCP: quantum critical point). Nuclear-spin-lattice relaxation rate 1/T-1 measurements revealed that the superconducting order occurs in the P range 1.36-1.84 GPa, with maximum T-c similar to 0.9 K around P-QCP similar to 1.36 GPa.

DOI： 10.1103/PhysRevB.80.184503

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DOI： 10.1143/JPSJ.78.115002

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The high quality single crystals of NpPd5Al2 with the body-centered tetragonal structure were grown by the Pb flux method. NpPd5Al2 was found to be the first Np-based heavy fermion superconductor with the relatively high critical temperature T-sc = 4.9 K. The upper critical field H-c2 is large and highly anisotropic. Corresponding to the heavy electronic state, the initial slope of H-c2 is large, but H-c2 at low temperatures is suppressed by the magnetic field, indicating a strong Pauli paramagnetic effect and the first-order transition at H-c2. These results imply that NpPd5Al2 is located at the proximity of the antiferromagnetic ordering, which might be hidden by the superconductivity. The d-wave superconductivity with a spin singlet state is most likely realized in NpPd5Al2.

DOI： 10.1088/0953-8984/21/16/164203

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Differential resistance spectra (dV/dI-V characteristics) have been measured for point contacts between the heavy-fermion superconductor (HFS) CePt3Si and a normal metal. Some contacts show a peak at V = 0 that is characteristic of HFS coexisting with a magnetic order such as UPd2Al3, UNi2Al3 and URu2Si2. The evolution of the peak occurs well above the antiferromagnetic transition temperature T-N similar to 2.2 K, so that the direct relationship with the magnetic transition is questionable. The half-width of the peak seems to reflect the crystal field splitting or the spin-wave gap as observed for the above-mentioned HFSs, possibly suggesting that some common scattering process induces the zero-bias peaks in these materials.

DOI： 10.1088/0953-8984/21/7/075703

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We have investigated the Fermi-surface (FS) properties in the Pr-based filled skutterudite PrOs4P12 and its reference compound LaOs4P12 by means of de Haas-van Alphen experiments and the band-structure calculations. The topology of FS in PrOs4P12 is close to that in the reference compound LaOs4P12, indicating a localized nature of 4f electrons in PrOs4P12. Whereas the localized nature of 4f electrons, we have confirmed a highly enhanced cyclotron effective mass of up to 18m(0) in PrOs4P12, which is enhanced about 3.8 times compared to that in LaOs4P12. No nesting property with q=(1,0,0) in the FS of PrOs4P12 has been confirmed in contrast to good nesting properties in PrFe4P12 and PrRu4P12 which exhibit unusual ordered states at low temperatures. A role of both the 4f electron's contributions and the FS nesting property for unusual phase transitions are discussed.

DOI： 10.1103/PhysRevB.79.035104

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We report on novel superconducting characteristics of the heavy fermion (HF) superconductor CePt3Si without inversion symmetry through Pt-195-NMR study on a single crystal with T-c = 0.46 K that is lower than T-c similar to 0.75 K for polycrystals. We show that the intrinsic superconducting characteristics inherent to CePt3Si can be understood in terms of the unconventional strong-coupling state with a line-node gap below T-c = 0.46 K. The mystery about the sample dependence oh T-c is explained by the fact that more or less polycrystals and single crystals inevitably contain some disordered domains, which exhibit a conventional BCS s-wave superconductivity (SC) below 0.8 K. In contrast, the Neel temperature T-N similar to 2.2 K is present regardless of the quality of samples, revealing that the Fermi surface responsible for SC differ from that for the antiferromagnetic order. These unusual characteristics of CePt3Si can be also described by a multiband model; in the homogeneous domains, the coherent HF bands are responsible for the unconventional SC, whereas in the disordered domains the conduction bands existing commonly in LaPt3Si may be responsible for the conventional s-wave SC. We remark that some impurity scatterings in the disordered domains break up the 4f-electrons-derived coherent bands but not others. In this context, the small peak in 1/T-1 just below T-c reported before [Yogi et al. (2004)] is not due to a two-component order parameter composed of spin-ringlet and spin-triplet Cooper pairing states, but due to the contamination of the disorder domains which are in the s-wave SC state.

DOI： 10.1143/JPSJ.78.014705

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DOI： 10.1103/PhysRevB.79.035104

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We report on novel superconducting characteristics of the heavy fermion (HF) superconductor CePt3Si without inversion symmetry through 195 Pt-NMR study on a high quality single crystal with T-c = 0.46 K that is lower than T-c similar to 0.75 K for polycrystals. The observation of short and long components in a nuclear relaxation time T-1 has revealed the presence of inhomogeneities of superconducting characteristics even in a single crystal. By discriminating the clean domain from the disordered domains, we show that the intrinsic superconducting characteristics inherent to CePt3Si can be understood in terms of the unconventional strong-coupling state with a line-node gap below T-c = 0.46 K. Furthermore, it was found that in some disordered domains that are inevitably contained in regardless of polycrystals or single crystals a conventional BCS s-wave superconducting state is realized below T-c similar to 0.75 K. We propose that these unusual superconducting and magnetic characteristics of CePt3Si can be described by a multiband model on the basis of the experimental facts.

DOI： 10.1088/1742-6596/150/5/052175

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We have investigated the differential conductance spectra of the point contacts between the heavy-fermion superconductor CeCoIn5 and Pt. Many of them show a double-maximum structure that indicates the superconducting energy gap (sic). The (sic) values derived using Blonder-Tinkham-Klapwijk model, however, varies from 0.47 to 0.77 meV, and yet they are within the scatter of the reported values. The evolution of (sic) below T-c is slow as compared with that of BCS gap probably reflecting the unconventional superconductivity in CeCoIn5. (c) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2008.06.036

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We measured the heat capacity of CelrSi(3)(100 mK<T<6K) under high pressure up to P = 1.38 GPa. The measurements have been used a quasiadiabatic method utilizing a CuBe piston-cylinder pressure cell in a dilution refrigerator. At 0 GPa, a sharp anomaly which indicates the antiferromagnetically transition is observed at T-N = 5 K. T-N decreases monotonically with increasing pressure up to P = 1.38 GPa. The magnetic entropy is released below T-N only 19% of Rln2 at 0GPa. And the magnetic entropy decreases with increasing pressure up to 1.38 GPa, 64% compared to that at 0GPa. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2008.06.033

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We report local magnetization measurements on the heavy fermion superconductor CeColn(5) using a inicro-Hall probe. Below a critical point T-0 (similar to 0.8 K), the local magnetization shows a clear jump at the Superconducting transition temperatures for both Hila and HIle, indicating that the phase transition at the upper critical field H-c2 becomes a first-order phase transition. In addition. we observed an undershoot behavior of magnetization jump above mu H-0 similar to 4.75 T (H parallel to c), which suggests a rapid change of textured superconducting structure with vortices and the nodal planes expected in the Fulde-Ferrell-Larkin-Ovchinnikov state. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2008.06.054

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High-quality single crystals of R3Al11 (R = La, Ce, Pr, and Nd) with the La3Al11-type orthorhombic crystal structure (space group Immm) have been grown by the Al-flux method. For Ce3Al(11), signatures for ferromagnetic and anti ferromagnetic orderings at T-C = 6.3 K and T-N = 3.2 K, respectively, have been observed in the magnetic susceptibility, magnetization, specific heat, and electrical resistivity. An anti ferromagnet Pr3Al11, on the other hand, exhibits two magnetic transitions at T-N1 = 12.6 K and T-N2 = 3.1 K. An antiferromagnet Nd3Al11 also exhibits multiple magnetic transitions at T-N1 = 13.2 K, T-N2 = 9.4 K, T-N3 = 2.9 K, and T-N4 = 1.77 K in zero magnetic field. The transition at T-N4 has a first-order character. The crystalline electric field (CEF) analysis of magnetic susceptibility, magnetization and specific heat data shows that the CEF splitting is larger for Ce3Al11 than for Pr3Al11 and Nd3Al11. The CEF ground state of Pr3Al11 is a singlet. Magnetic order occurs in this compound owing to the exchange mixing of the CEF around state and low-lying excited states. The ferromagnetic like component of the magnetization for H parallel to [010] is characteristic of R3Al11 (R = Ce, Pr, and Nd), which is most likely due to the Dzialoshinsky-Moriya interaction for two nonequivalent R atoms.

DOI： 10.1143/JPSJ.77.124704

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We observe several non-Fermi liquid behaviors in the normal-state transport properties of CeMIn5 (M: Rh and Co) under pressure at low temperatures: (1) The dc-resistivity shows T-linear dependence, p (x T. (2) The magnitude of Hall coefficient vertical bar R-H vertical bar increases rapidly with decreasing temperature, and reaches a value much larger than vertical bar 1/ne vertical bar at low temperatures. (3) The magnetoresistance displays T- and H-dependence that strongly violate Kohler's rule, and is well scaled by the tangent of the Hall angle, Delta rho(xx)rho(xx) alpha tan(2) Theta(H.) These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the quantum critical point. Since all of these salient features have been also reported for high-T-c cuprates, we infer that the non-Fermi liquid transport properties capture universal features of strongly correlated electron systems in the presence of strong anti ferromagnetic fluctuations. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2008.06.064

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We have Succeeded in observing the de Haas-van Alphen (dHvA) effect in LaFePO. the first reported iron-based superconductor in the iron-oxypnictide family. The four detected dHvA frequencies, which correspond to the cross-sectional areas of Fermi surfaces, approximately follow the 1/cos theta dependence,, where theta is the field-tilted angle from the [001] direction to the [100] and [110] directions in the tetragonal structure. This indicates that all the Fermi surfaces are nearly cylindrical, with the two-dimensional electronic state. The cyclotron effective mass, which was determined from the temperature dependence of the dHvA amplitude, is relatively large, ranging from 1.82 to 2.34m(0). The result of energy band structure calculation revealed that the conduction bands mainly consist of 3d electrons of Fe atoms.

DOI： 10.1143/JPSJ.77.113711

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The electronic properties in SmFe4P12 have been investigated by means of the de Haas-van Alphen effect, transverse magnetoresistance, Hall effect, and band structure calculation. We have found a markedly large anisotropy in the cyclotron effective mass of the 47th band Fermi surface despite its nearly spherical shape. Moreover, this mass enhancement in SmFe4P12 is robust against magnetic field. The transverse magnetoresistance increases nearly quadratically with magnetic field for all field directions; this is unexpected for an ordinary uncompensated metal. The Hall coefficient is found to be 4-fold enhanced at low temperature compared with that at room temperature. These anomalies in transport properties are ascribed to the stronger enhancement of the cyclotron effective mass of the 48th band Fermi Surface.

DOI： 10.1143/JPSJ.77.114705

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Specific heat measurements on a series of ternary compound RCu2Si2 (R: La, Pr, Nd, Sin, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) single crystals have been performed by the quasi-adiabatic heat Pulse method in the wide temperature range from 0.1 to 80 K. Almost all the compounds show antiferromagnetic orderings at low temperatures. We found the first-order like very sharp specific heat peaks in RCu2Si2 with R = Gd, Tb, Dy, Ho, and Er. Especially, the antiferromagnetic ordering in DyCu2Si2 is found to be a first-order transition. Front the analyses of the temperature dependence of magnetic entropy, we confirmed that the total splitting energy of the crystalline electric field (CEF) scheme of R3+ ion in RCu2Si2 is about 100 K in all the compounds studied here, except for YbCu2Si2. In addition, we observed the nuclear specific heat at low temperatures and estimated the magnitude of internal effective magnetic field H-eff at the nucleus.

DOI： 10.1143/JPSJ.77.104710

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We report a Ge-73 nuclear-quadrupole-resonance (NQR) Study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe3. The measurements of the Ge-73-NQR spectrum and the nuclear spin-lattice relaxation rate (1/T-1) have revealed that the unconventional superconductivity evolves inside a commensurate AFM phase around the pressure (P) where Neel temperature T-N exhibits its maximum at 8.5 K. The superconducting transition temperature T-SC has been found to be enhanced with increasing T-N, before reaching the quantum critical point at which the AFM order collapses. Above T-SC, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T similar to 2 K. accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the P-T phase diagram.

DOI： 10.1143/JPSJ.77.103710

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Language：English   Publisher：The Physical Society of Japan (JPS)  

We have succeeded in growing a high-quality single crystal of a non-4f reference compound YCu2Si2 for a heavy-fermion superconductor CeCu2Si2, and observed the de Haas-van Alphen (dHvA) oscillation. The detected dHvA branches in YCu2Si 2 indicate that the Fermi surfaces are multiply connected, and the dHvA frequencies are in the range from 9 × 106 to 2 × 108 Oe. These dHvA branches are found to be well explained by the results of energy band calculations. The corresponding cyclotron masses are light, ranging from 0.4 to 1:5m0, and are consistent with the electronic specific heat coefficient of 2.2 mJ/(K2·mol). ©2008 The Physical Society of Japan.

DOI： 10.1143/JPSJ.77.094702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

Specific-heat measurements were performed on a high-quality single crystal of CePt3Si without inversion symmetry in the tetragonal crystal structure. We observed distinct peaks in the specific-heat C at the superconducting transition temperature T-c = 0.46 K and the antiferromagnetic ordering temperature T-N = 2.25 K, compared to the previous data, indicating an improvement of the sample quality. The temperature dependence of the electronic specific-heat coefficient C-e/T below about 0.3 K is well described by the equation of C-e/T = gamma(s) + beta T-s with gamma(s) = 34.1 mJ/K-2.Mol and beta(s) = 1290 mJ/K-3.mol, evidencing the existence of line nodes in the superconducting energy gap. Furthermore, the electronic specific-heat coefficient gamma(s) in the superconducting state indicates a nonlinear magnetic field dependence gamma(s)(H) proportional to root H, which also supports the presence of line nodes.

DOI： 10.3938/jkps.53.1041

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We report pressure-induced superconductivity in antiferromagnetic cerium compounds and a ferromagnetic uranium compound, focusing on the relation between the superconducting state and the Fermi surface instability in CeRhIn5 and the huge upper critical field H-c2 in CeIrSi3 without inversion symmetry in the crystal structure. The pairing interaction is well correlated with ferromagnetism, as well as antiferromagnetism or antiferromagnetic fluctuations. In the recently discovered superconductor NpPd5Al2, superconductivity is found to be located in the vicinity of an antiferromagnetically ordered state. The upper critical field H-c2 is strongly supressed by the large paramagneic effect, and the corresponding magnetization curve indicates a step-like increase at H-c2, producing a first-order phase transition.

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An antiferromagnet CeRhIn5 is well known to be changed into a superconductor by applying pressure P. Its electronic state is also clarified to be changed at the critical pressure P-c similar or equal to 2.5 GPa under magnetic fields. We measured the low-temperature electrical resistivity of CeRhIn5 in magnetic fields up to 17T and at pressures LIP to 2.45 GPa, and constructed phase diagrams. At P = 2.45 GPa, which is close to P-c similar or equal to 2.5 GPa. there are four kinds of phases, namely, the paramagnetic, superconducting, superconducting and antiferromagnetic, and antiferromagnetic phases in the temperature vs magnetic field phase diagram. The antiferromagnetic phase is found to be induced in the superconducting phase under magnetic fields and expanded in magnetic fields higher than the upper critical field in Superconductivity. Interestingly, the anisotropy of the upper critical field in CeRhIn5 is found to be different from that in a similar non-magnetic heavy-fermion superconductor CeCoIn5, revealing the anisotropic paramagnetic Suppression of the upper critical field.

DOI： 10.1143/JPSJ.77.084708

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL INST OPTOELECTRONICS  

We studied the various kinds of electronic states in the f-electron systems of the cubic RX(3) and AnX(3) compounds and the tetragonal RTX(5) and AnTX(5) compounds (R: rare earth, An: Th, U, Np, Pu, T: transition metal, X: Al, Ga, In, Si, Ge, Sn) through the de Haas-van Alphen experiment and the energy band calculation. The former compounds are three dimensional in the electronic states, while the latter compounds are quasi-two dimensional. Pressure experiments were also carried out for antiferromagnets CeIn(3) and CeRhIn(5) to change the electronic state from the antiferromagnetically ordered state to the non-magnetic state, crossing the critical pressure region where the Neel temperature becomes zero. Around this critical pressure region, d-wave superconductivity is induced, and a marked change of the Fermi surface properties from the 4-localized state to the 4f-itinerant state occurs at this critical pressure, revealing the first-order phase transition.

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We measured low-temperature electrical resistivity in a magnetic field as a function of pressure, and studied the superconducting property of CeIrSi3 with a non-centrosymmetric tetragonal structure. CeIrSi3 is an antiferromagnet with a Neel temperature T-N = 5.0 K at ambient pressure, but the antiferromagnetic ordering disappears completely at a pressure P-c = 2.25 GPa. Superconductivity appears in a wide pressure region from 1.8 to about 3.5 GPa, with a maximum transition temperature T-sc similar or equal to 1.6 K at P-c* similar or equal to 2.63 GPa. At around P-c*, the upper critical field H-c2 for the magnetic field H along the [0 01] direction is not destroyed by spin polarization based on Zeeman coupling but possesses an upturn curvature below 1K, revealing a divergent tendency of H-c2 at P-c*, with a huge H-c2(0) similar or equal to 450 kOe. On the other hand, the upper critical field for H parallel to [110] indicates the tendency of Pauli paramagnetic suppression, with H-c2(0) = 95 kOe at 2.65 GPa. This might be a combined phenomenon between the electronic instability at P-c* and the characteristic superconducting property without inversion symmetry in the tetragonal structure.

DOI： 10.1143/JPSJ.77.073705

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In quasi-two-dimensional Ce(Ir,Rh)In(5) system, it has been suggested that the phase diagram contains two distinct domes with different heavy-fermion superconducting states. Here, we report the systematic pressure dependence of the electron transport properties in the normal state of CeRh(0.2)Ir(0.8)In(5) and CeIrIn(5), which locates in first and second superconducting domes, respectively. We observed non-Fermi liquid behavior at low temperatures in both compounds, including nonquadratic T dependence of the resistivity, large enhancement of the Hall coefficient, and the violation of the Kohler rule in the magnetoresistance. We show that the cotangent of the Hall angle cot Theta(H) varies as T(2), and the magnetoresistance is quite scaled well by the Hall angle as Delta rho(xx)/rho(xx)proportional to tan(2) Theta(H). The observed transport anomalies are common features of CeMIn(5) (M=Co, Rh, and Ir) and high-T(c) cuprates, which suggest that the anomalous transport properties observed in CeIrIn(5) are mainly governed by the antiferromagnetic spin fluctuations not by the Ce-valence fluctuations, which have been proposed to be the possible origin for the second superconducting dome.

DOI： 10.1103/PhysRevB.77.214504

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We grew single crystals of non-centrosymmetric compounds CeTSi3 and CeTGe3 (T: transition metal), and studied the magnetic properties by measuring the electrical resistivity, magnetic susceptibility and magnetization. We also studied the effect of pressure on the electronic states in antiferromagnets CeTGe3 (T: Co, Rh, Ir) by measuring the resistivity under pressure. No noticeable change of the Neel temperature was observed up to 8 GPa in CeRhGe3 and CeIrGe3, which are far from the magnetic quantum critical point. On the other hand, the Neel temperature in CeCoGe3 was strongly decreased as a function of pressure, and pressure-induced superconductivity was observed in the pressure region from 5.4GPa to about 7.5 GPa. The slope of upper critical field H,2 at 6.5 GPa is found to be extremely large, with an upturn curvature of H,2 with decreasing temperature: -dH,2/dT = 200kOe/K at the superconducting transition temperature T,,, = 0.69 K, revealing unconventional superconductivity.

DOI： 10.1143/JPSJ.77.064716

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We succeeded in growing single crystals of LaTGe3 (T: Fe, Co, Rh, Ir) and PrCoGe3 with the non-centrosymmetric tetragonal crystal structure, and studied the split Fermi surface properties and the magnitude of the antisymmetric spin-orbit interaction 2 vertical bar alpha p perpendicular to vertical bar. The 2 vertical bar alpha p perpendicular to vertical bar value is found to vary when LaTGe3 is changed from T = Co, Rh to Ir, but remains unchanged in LaIrX3 from X = Si to Ge. It is found that this 2 vertical bar alpha p perpendicular to vertical bar value is large in LaIrSi3 and LaIrGe3: 2 vertical bar alpha p perpendicular to vertical bar = 460 K in LaCoGe3, 510 K in LaRhGe3, 1100 K in LaIrSi3, and 1090 K in LaIrGe3 for the main outer orbits named alpha of bands 69 and 70 electron Fermi surfaces, for example. This is due to the large effective atomic number of Ir and a large distribution of the radial wave function of Ir-5d electrons close to the nuclear center, compared with those of Co and Rh. In the case of a paramagnet PrCoGe3 and LaFeGe3 with the relatively large cyclotron mass, the corresponding 2 vertical bar alpha p perpendicular to vertical bar value is found to become small: 2 vertical bar alpha p perpendicular to vertical bar= 280 and 460 K for main orbits ot in PrCoGe3 and LaCoGe3, respectively, and 130 K for main orbits in LaFeGe3.

DOI： 10.1143/JPSJ.77.064717

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We succeeded in growing a single crystal of a layered compound Lu2Rh3Ga9 with an Y2Co3Ga9-type orthorhombic crystal structure by the Ga-flux method. The lattice, positional, and thermal parameters were determined by single-crystal x-ray diffraction measurement. We also measured the electrical resistivity, specific heat, and de Haas-van Alphen (dHvA) effect. The detected dHvA branches were well explained by the results of full potential linear augmented plane-wave (LAPW) energy band calculations. The electronic state was found to be quasi-two-dimensional, indicating nearly cylindrical Fermi surfaces along the [001] direction.

DOI： 10.1143/JPSJ.77.064708

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High-quality single crystals of rare earth and actinide compounds were grown by using several kinds of techniques such as the Czochralski method, flux method, chemical transport method and Bridgman method, together with purification of a uranium ingot by the solid state electrotransport method. For these single crystals, the de Haas-van Alphen experiment was carried out to clarify the Fermi surface properties, focusing on the quasi-two-dimensional electronic state of RTX(5) (R: rare earth, T: transition metal, X: In and Ga) and AnTX(5) (An: Th, U, Np and Pu), which were compared with the results of the energy band calculation. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2007.09.032

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A layered compound CePd5Al2, which is an analog of a heavy fermion superconductor NpPd5Al2, is found to be an antiferromagnet with an easy-axis along the tetragonal [001] direction but becomes superconductive in the pressure region from 9 to 12GPa, with the superconducting transition temperature, T-sc = 0.57 K and the upper critical field at 0 K, H-c2(0) = 2.5 kOe, at 10.8 GPa. The quasi-two dimensional Fermi surfaces are also theoretically calculated for CePd5Al2 on the basis of the 4f-itinerant band model.

DOI： 10.1143/JPSJ.77.043701

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We report on the pressure (P)-induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their border at zero magnetic field. The nuclear-quadrupole-resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with T-c similar to 2.1 K at P = 2.05 GPa and the AFM quantum phase transition (QPT) occurs near P = 2.1 GPa. These results reveal the existence of the tetracritical point in the P-T phase diagram of AFM and SC in CeRnIn5. We also found the gapless nature in the uniformly coexisting phase of AFM and SC, indicating an intimate relationship between AFM and SC. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.062

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report a Si-29 NMR study on the pressure-induced superconductivity (SC) in an antiferromagnetic (AFM) heavy-fermion compound CeIrSi3 without inversion symmetry. In the SC state at P=2.7-2.8 GPa, the temperature (T) dependence of the nuclear-spin lattice relaxation rate 1/T-1 below T-c exhibits a T-3 behavior without any coherence peak just below T-c, revealing the presence of line nodes in the SC gap. In the normal state, 1/T-1 follows a root T-like behavior, suggesting that the SC emerges under the non-Fermi-liquid state dominated by AFM spin fluctuations enhanced around a quantum critical point. The reason why the maximum T-c in CeIrSi3 is relatively high among the Ce-based heavy-fermion superconductors may be the existence of the strong AFM spin fluctuations. We discuss the comparison with the other Ce-based heavy-fermion superconductors.

DOI： 10.1103/PhysRevLett.100.107003

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We report on pressure-induced unconventional superconductivity (SC) in the heavy-fermion (HF) antiferromagnet CeIn3 by means of nuclear-quadrupole- resonance (NQR) studies conducted under a high pressure. The temperature (T) and pressure (P) dependences of the In-NQR spectra have revealed a first-order quantum-phase transition (QPT) from antiferromagnetism (AFM) to paramagnetism (PM) at a critical pressure Pc =2.46 GPa at which AFM disappears with a minimum value of TN (Pc) =1.2 K. High-energy x-ray scattering measurements under P show a progressive decrease in the lattice density without any change in the crystal structure, whereas an increase in the NQR frequency (νQ) indicates an increase in the hybridization between 4f electrons and conduction electrons, which stabilizes the HF-PM state. This competition between the AFM phase where TN is reduced and the formation of the HF-PM phase triggers the first-order QPT at Pc =2.46 GPa. Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that unconventional SC occurs in both phases of AFM and PM. The measurements of the nuclear spin-lattice relaxation rate 1/T1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. Remarkably, the significant increase in 1/T1 upon cooling in the AFM phase has revealed the development of low-lying magnetic excitations down to Tc in the AFM phase
it is indeed relevant to the onset of the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T1 decreases without the coherence peak just below Tc, followed by a power-law-like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, Tc has a peak around Pc in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of Tc =230 mK around Pc, indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3. These phenomena observed in CeIn3 should be understood in terms of the first-order QPT because these new phases of matter are induced by applying P. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, Pc =2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical point from AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.064508

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We have carried out neutron diffraction experiments on Ce2Ni3Ge5 single crystal. Ce2Ni3Ge5 orders antiferromagnetically below T-N=5K and exhibits a successive transition at T* = 4.3 K. We have confirmed that the ground state antiferromagnetic structure is characterized with the propagation vector q = [010]. We have revealed that this magnetic structure stabilizes only below V = 4.3 K from the simultaneous neutron diffraction and electrical resistivity measurements, contrary to the previously reported neutron powder diffraction result. From the analysis of magnetic reflection intensities, we suggest that the ground state magnetic structure is a canted AF structure, where the moments orient about 200 tilted from the a-axis in the ab-plane. The obtained AF components are 0.45 mu(B)/Ce along the a-axis and 0.15 mu(B)/Ce along the b-axis. It is suggested that the high temperature phase is characterized with another magnetic phase having a different propagation vector, which is not determined in the present study. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.jallcom.2007.04.191

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We report the first successful observation of the de Haas-van Alphen (dHvA) effect in Eu-based filled skutterudite EuRu4Sb12 which shows a ferromagnetic transition at T-C = 3.3 K. The dHvA frequencies and those angular dependences are highly different from those for the trivalent compounds such as LaRu4Sb12 and PrRu4Sb12. This fact is consistent with the results of magnetic susceptibility and the X-ray absorption near edge spectroscopy measurements which have revealed a nearly divalent Eu electronic configuration. The cyclotron effective masses have been estimated ranging from 1.6(m0) to 2.6(m0).

DOI： 10.1143/JPSJS.77SA.297

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High-quality single crystals of Ce3Al11 with the orthorhombic crystal structure have been grown by the Al-flux method. Signatures for ferromagnetic and antiferromagnetic orderings at T-C = 6.3K and T-N = 3.2K, respectively, have been observed in the electrical resistivity. On application of pressure, the Neel temperature T-N decreases rapidly and goes to zero around 3GPa. On the other hand, the Curie temperature T-C is found to be robust against pressure up to 4GPa. Further, dHvA oscillations have been obtained for magnetic field along the [0 1 0] direction. A cyclotron mass m(c)* as large as 28m(0) (m(0): rest mass of an electron) has been observed for one of the dHvA branches, indicating the heavy fermion nature of Ce3Al11.

DOI： 10.1143/JPSJS.77SA.356

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We have succeeded in observing the de Haas-van Alphen effect in LaOs4P12 which is a superconductor with the transition temperature T-C = 2.0 K and a reference compound for PrOs4P12. We have found the multiply-connected and almost spherical Fermi surfaces whose cyclotron effective masses are ranging 1.1-4.7m(0). The Fermi surface topology is close to that of PrOs4P12, indicating the localized nature of 4f-electrons in PrOs4P12. From the comparison with LaOs4P12, the large mass enhancement in PrOs4P12 has been clarified.

DOI： 10.1143/JPSJS.77SA.219

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We have succeeded in observing the de Haas-van Alphen effect in PrOs4P12 which shows no anomaly down to 50 mK in contrast to PrFe4P12 and PrRu4P12. The Fermi surface (FS) topology is reasonably explained by the energy band structure calculation based on a full potential linearized augmented-plane-wave method within the local-density-approximation. Whereas the localized nature of 4f-electrons, we have confirmed a highly enhanced cyclotron effective mass up to 18m(0) in PrOs4P12, which is enhanced 3.8 times compared to that of LaOs4P12. No nesting property with q = (1, 0, 0) in the FS of PrOs4P12 has been confirmed, which suggests both the 4f-electron's contribution and the FS nesting property play the role for the phase transitions in PrFe4P12 and PrRu4P12.

DOI： 10.1143/JPSJS.77SA.108

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We measured the electrical resistivity, specific heat, magnetic susceptibility and magnetization in the first Np-based superconductor NpPd5Al2 with the tetragonal crystal structure. NpPd5Al2 is a paramagnet and becomes the superconductivity at T-c = 4.9 K. The large electronic specific heat coefficient of gamma = 200mJ/K(2)mol at T-c indicates that NpPd5Al2 is a heavy fermion superconductor. The upper critical field Hc2 is large and highly anisotropic: H-c2(0) = 37 kOe for H parallel to [100] and H-c2(0) = 143 kOe for H parallel to [001]. Although the initial slope of H-c2 at Tc is very large, H-c2 is strongly suppressed against the magnetic field for both field direction, indicating the existence of strong Pauli paramagnetic effect. Furthermore, the magnetization curve shows the step-like behaviors at H-c2, corresponding to the first order transition. The d-wave superconductivity with the spin-singlet state is most likely realized in NpPd5Al2.

DOI： 10.1143/JPSJS.77SA.159

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We have performed de Haas-van Alphen (dHvA) experiments using micro-cantilever on small single crystal of LaFeGe3 with longest dimension less than 0.1 mm. Detected dHvA frequencies using micro-cantilever shows a good agreement with the result of the band calculation. The micro-cantilever is a hopeful device to detect the dHvA effect for a very small single crystals less than 0.1mm

DOI： 10.1143/JPSJS.77SA.345

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The upper critical field Hc(2) in superconductivity was investigated for CePt3Si and CeIrSi3 without inversion symmetry in the tetragonal structure. A significant anisotropy of Hc(2) between H vertical bar vertical bar [0 0 1] and H vertical bar vertical bar [1 0 0] was not observed in CePt3Si even at 0.6 GPa as well as ambient pressure, where the Neel temperature with T-N = 2.3 K at ambient pressure becomes zero at 0.6 GPa. The similar result was observed at 1.95 GPa in CeIrSi3, where antiferromagnetism and superconductivity coexist, while a large anisotropy of Hc(2) in CeIrSi3 was observed with increasing pressure: Hc(2)(0) = 300-400 kOe for H vertical bar vertical bar [0 0 1] and Hc(2)(0) = 95 kOe for H vertical bar vertical bar [1 1 0] at 2.65 GPa, which is higher than the critical pressure P-c = 2.25 GPa. A large value of Hc(2) for H vertical bar vertical bar [0 0 1] in CeIrSi3 might become an experimental evidence of the spin-triplet superconductivity in the non-centrosymmetric structure. It is also remarkable that CeIrSi3 is a strong coupling superconductor and the electronic specific heat coefficient is approximately unchanged as a function of pressure even at P-c, which is highly different from the divergent mass enhancement at Pc in a pressure-induced heavy fermion superconductor CeRhIn5.

DOI： 10.1143/JPSJS.77SA.37

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We succeeded in growing a high-quality single crystal of URu2Si2 by the Czochralski pulling method and applying the solid state electro-transport method under ultrahigh vacuum. The sample quality strongly depends on the position in the ingot. For some parts of this ingot, the electrical resistivity, specific heat and de Haas-van Alplhen effect were measured. The electrical resistivity of the surface sample clearly indicates a T-linear temperature dependence below 5 K. The mean free path in this sample was determined by the de Haas-van Alphen effect to be 11000 angstrom.

DOI： 10.1143/JPSJS.77SA.362

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We have carried out the electrical resistivity measurements under high pressures and high magnetic fields in NpPd5Al2 in order to investigate a quantum critical behavior and the stability of the superconducting phase. A T-linear dependence of the electrical resistivity is changed into the Fermi liquid relation of rho similar to AT(2) under the magnetic fields, and A value indicates a divergent feature around the upper critical field H-c2, indicating the existence of a field-tuned quantum critical point (QCP) around H-c2. With increasing pressure, the superconducting transition temperature T-sc decreases and becomes zero above 5.7 GPa, together with a decrease of the upper critical field, indicating that the electronic state of NpPd5Al2 is located in the vicinity of QCP at ambient pressure and deviates from QCP with increasing pressure. Furthermore, we have constructed the superconducting phase diagram at 3.71 GPa.

DOI： 10.1143/JPSJS.77SA.339

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We investigated the pressure-induced superconductor CeIrSi3 without inversion center under high pressure. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure of the antiferromagnetic state was determined to be P-c = 2.25 GPa. The heat capacity C-ac shows both antiferromagnetic and superconducting transitions at pressures close to P-c. The co-existence of the antiferromagnetism and superconductivity is discussed. The superconducting region is extended up to about 3.5 GPa. The superconducting transition temperature T-sc shows a maximum value of 1.6 K around 2.5 - 2.7 GPa. At 2.58 GPa, a large heat capacity anomaly was observed at T-sc = 1.59 K. The jump of the heat capacity in the form of Delta C-ac/C-ac(T-sc) is 5.7 +/- 0.1. This is the largest observed value among all superconductors studied previously, suggesting the strong-coupling superconductivity in CeIrSi3.

DOI： 10.1088/1742-6596/121/5/052001

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We present a study of thermoelectric coefficients in CeCoIn5 down to 0.1 K and up to 16 T in order to probe the thermoelectric signatures of quantum criticality. In the vicinity of the field-induced quantum critical point, the Nernst coefficient nu exhibits a dramatic enhancement without saturation down to the lowest measured temperature. The dimensionless ratio of the Seebeck coefficient to the electronic specific heat shows a minimum at a temperature close to threshold of the quasiparticle formation. Close to T-c(H), in the vortex-liquid state, the Nernst coefficient behaves anomalously in puzzling contrast with other superconductors and standard vortex dynamics.

DOI： 10.1103/PhysRevLett.99.147005

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We report our measurements of transport coefficients of quasi-2D HF CeRIn5 in the normal state, in the vicinity of a QCP and in the superconducting state. In the normal state, we observed a T-linear resistivity, a T-2-dependence of cot theta(H) (theta(H) is the Hall angle), the violation of Kohler's rule, and a giant Nernst coefficient. In the superconducting state, on the other hand, we found a rapid increase of the quasiparticle (QP) mean free path as the temperatures is reduced below T-c. The density of states (DOS) of delocalized QPs obtained from the thermal Hall coefficient is consistent with a d-wave pairing symmetry. Moreover, the angular dependence of thermal conductivity indicates that the gap function has a d-wave symmetry with line nodes perpendicular to the ab-plane. These results bear a striking resemblance to those obtained for the high-T-c cuprates. This similarity implies that the fluctuation and excitation spectrum near a 2D antiferromagnetic QCP could be universal. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.physc.2007.04.004

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We studied the pressure-induced superconductor CeIrSi3 with the non-centrosymmetric tetragonal structure under high pressure. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure was determined to be P-c = 2.25 GPa, where the antiferromagnetic state disappears. The heat capacity C-ac shows both antiferromagnetic and superconducting transitions at pressures close to P, On the other hand, the superconducting region is extended to high pressures of up to about 3.5 GPa, with the maximum transition temperature T-sc = 1.6 K around 2.5-2.7GPa. At 2.58GPa, a large heat capacity anomaly was observed at T-sc = 1.59K. The jump of the heat capacity in the form Of Delta C-ac/C-ac(T-sc) is 5.7 +/- 0.1. This is the largest observed value among previously reported superconductors, indicating the strong-coupling superconductivity. The electronic specific heat coefficient at T-sc is, however, approximately unchanged as a function of pressure, even at P-c.

DOI： 10.1143/JPSJ.76.083706

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We measured the electrical resistivity under pressure for an antiferromagnet CeCoGe3 without inversion symmetry in the tetragonal crystal structure. The Neel temperature T-N1 = 21 K at ambient pressure decreases monotonically with increasing pressure, and becomes zero at about 5.5 GPa. Superconductivity appears above 4.3GPa, with a superconduting transition temperature T-SC = 0.72 K and a large upper critical field H-c2(0) = 7 T at 5.6 GPa. The large upper critical field H-c2 (0) =7 T exceeds the Pauli limitting field H-p (similar or equal to 1.86T(SC))=1.3 T as in CePt3Si, CeRhSi3 and CeIrSi3. The large slope of H-c2 at T-SC, -dH(c2)/dT = 18 T/K, at 5.6 GPa indicates the heavy-fermion superconductivity in CeCoGe3.

DOI： 10.1142/S0217979207044287

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We report on a pressure-temperature phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in CeRhIn5 studied by the nuclear-quadrupole-resonance measurements under pressure. It is demonstrated that an AFM phase transition takes place inside the superconducting state. This result reveals that a tetracritical point exists in the phase diagram of AFM and SC at zero magnetic field. The finding of unconventional SC characteristics in the uniformly coexisting phase of AFM and SC suggests that both phases may be mediated by the same magnetic interaction.

DOI： 10.1103/PhysRevB.76.020509

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We succeeded in growing a high-quality single crystal of ThRhIn5 with the HoCoGa5-type tetragonal crystal structure by the In-flux method. The lattice parameters, positional parameters and thermal parameters were determined from single-crystal x-ray diffraction measurements. We also measured the electrical resistivity and de Haas-van Alphen (dHvA) effect. Main dHvA branches are very similar to those of the 4f-itinerant heavy fermion superconductor CeCoIn5, but the cyclotron effective masses are by one to two orders of magnitude smaller than those of CeCoIn5. These Fermi surface properties are well explained by the FLAPW energy band calculations.

DOI： 10.1143/JPSJ.76.064712

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We report on antiferromagnetic (AF) properties of pressure-induced superconductivity in CeNiGe3 via the Ge-73 nuclear-quadrupole-resonance (NQR) measurements under pressure (P). The NQR-spectrum measurements have revealed that the incommensurate antiferromagnetic ordering is robust against increasing P with the increase of ordered moment and ordering temperature. Nevertheless the measurements of nuclear spin-lattice relaxation rate (1/T-1) have pointed to the onset of superconductivity as a consequence of Ce-4f electrons delocalized by applying P. The emergence of superconductivity under the development of AF order suggests that a novel type of superconducting mechanism works in this compound. (c) 2006 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.883

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We investigated the magnetic properties of CeTSi3 (T: Ru, Os, Co, Rh, Ir, Pd and Pt) and CeTGe3 (T: Co, Rh and Ir) by measuring their electrical resistivity and magnetic susceptibility. CeRuSi3, CeOsSi3 and CeCoSi3 do not order magnetically, with a large Kondo temperature of about 200 K. The other compounds order antiferromagnetically, and are very similar to each other in their magnetic and electronic properties, which is related to a large crystalline electric. field (CEF) splitting energy of the 4f electron, about 500K in CeIrSi3. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2006.10.055

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We report on the evolution of the Hall effect in heavy fermion compounds CeMIn5 (M = Co, Rh), ranging from antiferromagnetic metal to Fermi liquid regime through non-Fermi liquid regime by applying pressure. We found that anomalous transport properties of CeMIn5 are strikingly similar to that of high-T-c cuprates. We also found that the magnitude of Hall coeffi. cient appears to diverge near an antiferromagnetic quantum critical point. These results strongly suggest that unusual transport properties of CeMIn5 are dominated by anisotropic scattering due to strong spin. uctuations. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.028

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To investigate the quasiparticle dynamics in the superconducting state of quasi-two dimensional heavy fermion superconductor CeCoIn5, thermal conductivity tensor is measured. We obtained the quasiparticle mean free path and the density of states separately by using the combination of longitudinal thermal conductivity and thermal Hall angle. The quasiparticle mean free path increases dramatically below T-c in zero magnetic field. The density of states and the scaling relation of thermal Hall conductivity are consistent with d-wave symmetry. We also argue that CeCoIn5 is in the superclean regime. These results highlight the anomalous superconducting state in CeCoIn5 with striking similarities with high-T-c cuprates. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.154

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The Josephson effect between a single-crystal CeIrIn5 and an s-wave superconductor has been investigated for current. ows parallel to the [1 0 0] and [1 1 0] axes of CeIrIn5. The magnetic-field modulation of the Josephson critical current has shown a nearly ideal Fraunhofer pattern in the [1 0 0] direction and a small deviation from that pattern in the [1 1 0] direction. The clear anisotropy, which has been reported for YBa2Cu3O7-delta indicating the d- wave superconductivity, was not observed in this study. (c) 2006 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.245

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We measured the electrical resistivity and AC-specific heat for a canted ferromagnet CePtAl under pressures using a diamond-anvil pressure cell. With increasing pressure, the magnetic ordering temperature T-C1 increases monotonously, becomes constant above 8GPa and then starts to decrease steeply in a narrow pressure region from 10.3 to 10: 9 GPa, indicating the first-order like phase transition. The similar pressure dependence of T-C1 was obtained in the AC-specific heat measurement. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.056

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We report the synthesis of three new Yb-based compounds, Yb8Ag18.5Al47.5 (Yb8Cu17Al49-type, tetragonal tI74-14/mmm), Yb2Pd2Cd (Mo2B2Fe-type, tetragonat tP10-P4/mbm) and Yb1.35Pd2Cd0.65 (MnCu2Al-type, cubic cF16-Fm (K) over barm). The crystal symmetry of these compounds has been determined and the complete structural characterisation carried out by single crystal and powder diffraction techniques. Two symmetry in-equivalent sites are available for the Yb ions in Yb8Ag18.5Al47.5 and Yb1.35Pd2Cd0.65. The 4f levels of the Yb ions are appreciably hybridised in Yb8Ag18.5Al47.5 and to a lesser extent in Yb2Pd2Cd as inferred from the magnetisation and heat capacity data. Signatures of heavy fermion behaviour are observed in the heat capacity data of Yb2Pd2Cd in which the heat capacity, C/T, increases at low temperatures attaining a value of approximate to 600 mJ/mol K-2 at 1.8 K. The electrical resistivity of Yb2Pd2Cd follows a linear variation with temperature, T, between 1.4 and 5 K, thus indicating a possible non-Fermi liquid behaviour. In contrast, Yb ions are trivalent in Yb1.35Pd2Cd0.65 and order magnetically near 1.4 K. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.05.013

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An antiferromagnet CeNiGe3, which exhibits a quantum critical point at PC ∼ 6 - 7 GPa, shows the superconductivity in wide pressure range of 1.7 - 9.3 GPa. In addition to the superconductivity around PC, the sharp superconducting transition can be observed by both the resistivity and the susceptibility measurements at lower pressure region far apart from PC, where 4f-localized picture seems to be still dominant. Such a superconductivity is a first example in the f-electron systems. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.147

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We report on the pressure dependence of the Hall coefficient RH in quasi-2D heavy fermion CeCoIn5. At ambient pressure, below a temperature associated with the emergence of non-Fermi liquid properties, RH is anomalously enhanced. We found that the restoration of the Fermi liquid state with applied pressure leads to a gradual suppression of this dramatic enhancement. Moreover, the enhancement in RH was found to be confined to an intermediate temperature window, where inelastic electron-electron scattering is dominant. Our results strongly support the presence of cold and hot spots on the Fermi surface probably due to anisotropic scattering by antiferromagnetic fluctuations, which may also prove relevant for the debate on the anomalous normal-state properties of high-T-c cuprates.

DOI： 10.1143/JPSJ.75.023705

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We have studied a change of the electronic states in antiferromagnets CeIn3, CeRhIn5 and CePt3Si via the de Haas-van Alphen experiments. The critical pressure P-c, where the Neel temperature becomes zero, is P-c similar or equal to 2.5 GPa in CeIn3 with the cubic crystal structure, in which the narrow pressure region superconductivity appears below a superconducting transition temperature T-sc = 0.2 K. In the pressure region P > P-c, we detected a main Fermi surface with the cyclotron mass m*(c) = 53m(0), which most likely corresponds to a nearly spherical Fermi surface in the paramagnetic state, namely a 4f-itinerant Fermi surface. The Fermi surface in the antiferromagnet CeRhIn5 with the tetragonal crystal structure is similar to that of LaRhIn5, consisting of two kinds of nearly cylindrical Fermi surfaces. We observed a drastic change of the Fermi surface from 4f-localized (LaRhIn5) to 4f-itinerant (CeCoIn5) Fermi surfaces at P-c similar or equal to 2.4 GPa. The cyclotron mass increases intensively above 1.6 GPa where superconductivity sets in. CePt3 Si with the tetragonal crystal structure without inversion symmetry is highly different from CeIn3 and CeRhIn5 in magnetism and superconductivity. It orders antiferromagnetically below T-N = 2.3 K and becomes superconductive below T-sc = 0.6 K at ambient pressure. With increasing pressure, the cyclotron mass is found to be reduced, together with a steep decrease of T-N and Tsc, where P-c is most likely about 1.5 GPa in CePt3Si. The heavy fermion state Of CePt3Si is realized at ambient pressure. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.04.101

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We report the measurements of the Si-29 Knight shift K-29 on the noncentrosymmetric heavy-fermion compound CePt3Si in which antiferromagnetism (AFM) with T-N = 2.2 K coexists with superconductivity (SC) with T-c = 0.75 K. Its spin part K-29(s), which is deduced to be K-s(c) >= 0.11 and 0.16% at respective magnetic fields H = 2.0061 and 0.8671 T, does not decrease across the superconducting transition temperature Tc for the field along the c-axis. The temperature dependence of nuclear spin-lattice relaxation of Pt-195 below T-c has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt3Si.

DOI： 10.1143/JPSJ.75.013709

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We report the novel phase diagram of superconductivity (SC) and anti ferromagnetism (AFM) in heavy-fermion (HF) pressure(P)-induced superconductors CeRhIn5 and CeIn5 through nuclear-quadrupole-resonance (NQR) measurements under P. The P-induced superconductivity in CeRhIn5 coexists with AFM on a microscopic level in P = 1.5-1.9 GPa. By contrast, in CeIn3, the P-induced phase separation of AFM and paramagnetism (PM) takes place without any trace of a quantum phase transition. The outstanding finding is that SC sets in at both the phases magnetically separated into AFM and PM in P=2.28-2.5 GPa. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.10.043

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We report on magnetic and novel superconducting properties in heavy-fermion (HF) noncentrosymmetric compound CePt3Si via the measurement of Pt-195 nuclear spin-lattice relaxation rate 1/T-1. This compound reveals the uniform coexistence of antiferromagnetism (T-N = 2.2 K) and superconductivity (T-c =0.75 K). CePt3Si is the first HF superconductor that reveals a peak in 1/T-1 just below T-c and, additionally, does not follow the T-3 law that was observed for most unconventional HF superconductors. The novel relaxation behavior found below T-c may be relevant with a possible novel SC state being realized in the noncentrosymmetric CePt3Si. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.10.070

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DOI： 10.1080/13642819708202330

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We report on a study of thermal Hall conductivity κxy in the superconducting state of CeCoIn5. The scaling relation and the density of states of the delocalized quasiparticles, both obtained from κxy, are consistent with d-wave superconducting symmetry. The onset of superconductivity is accompanied by a steep increase in the thermal Hall angle, pointing to a striking enhancement in the quasiparticle mean free path. This enhancement is drastically suppressed in a very weak magnetic field. These results highlight that CeCoIn5 is unique among superconductors. A small Fermi energy, a large superconducting gap, a short coherence length, and a long mean free path all indicate that CeCoIn5 is clearly in the superclean regime (εF Δ ξ), in which a peculiar vortex state is expected. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.214515

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We report on a study of thermal Hall conductivity kappa(xy) in the superconducting state of CeCoIn5. The scaling relation and the density of states of the delocalized quasiparticles, both obtained from kappa(xy), are consistent with d-wave superconducting symmetry. The onset of superconductivity is accompanied by a steep increase in the thermal Hall angle, pointing to a striking enhancement in the quasiparticle mean free path. This enhancement is drastically suppressed in a very weak magnetic field. These results highlight that CeCoIn5 is unique among superconductors. A small Fermi energy, a large superconducting gap, a short coherence length, and a long mean free path all indicate that CeCoIn5 is clearly in the superclean regime (epsilon(F)/Delta <center dot/xi), in which a peculiar vortex state is expected.

DOI： 10.1103/PhysRevB.72.214515

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We have succeeded in growing a high-quality single crystal of ThIn3 with the cubic structure by the Influx method and measured the electrical resistivity, magnetic susceptibility and de Haas-van Alphen (dHvA) effect. Several dHvA branches were observed, ranging from 5.2 x 10(6) to 1.7 x 10(8) Oe. The Fermi surface consists of a nearly spherical Fermi surface and a multiply-connected Fermi surface. The corresponding cyclotron effective masses are small, ranging from 0.31 to 1.4 m(0). These Fermi surface properties are well explained by the energy band calculations based on the FLAPW method.

DOI： 10.1143/JPSJ.74.3276

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DOI： 10.1143/JPSJ.74.3393

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We have studied a change of the Fermi surface in an antiferromagnet CeIn3 via the de Haas-van Alphen experiment under pressure up to 3 GPa. With increasing pressure P, the Neel temperature T-N = 10 K decreases and becomes zero at a critical pressure P-c similar or equal to 2.6 GPa. In the pressure region P > P,, we have observed a large main Fermi surface named a, which indicates that the electronic state of 4f electron in CeIn3 changes from localized to itinerant at P-c, as observed in the similar antiferromagnets CeRh2Si2 and CeRhIn5. The cyclotron effective mass m(c)(*) of this main Fermi surface is extremely enhanced around P-c: m(c)(*) similar or equal to 60m(0) at 2.7 GPa for the magnetic field along the (100) direction.

DOI： 10.1143/JPSJ.74.3016

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Josephson critical current I-c between a single crystal CePt3Si and Al has been measured for the junctions on the CePt3Si surface perpendicular to the a and c axes. In the magnetic-field dependence of I-c a dominant maximum peak at zero field has been observed only for the junction on the a-axis face thus far, indicating that the Josephson effect is allowed at least for current flow parallel to the a axis. This result places a restriction on the representations of the order parameter in the noncentrosymmetric superconductor CePt3Si.

DOI： 10.1143/JPSJ.74.3041

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We have measured the ultrasound velocity of quasi-two-dimensional superconductor CeCoIn5 with extremely large Pauli paramagnetic susceptibility. The results indicate that the new high field superconducting phase, which is revealed by the recent heat capacity measurements, is characterized by the unusual softening of flux line lattice. The softening is most likely due to the collapse of the flux line lattice tilt modulus and transition to quasi-two-dimensional vortex state. These results provide a strong evidence that the high field phase is the Fulde-Ferrell-Larkin-Ovchinnikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicularly to the vortices. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2005.02.018

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We show that in recently discovered heavy fermion superconductors, quasi two-dimensional CeCoIn5 and skutterudite PrOs4Sb12, multiple superconducting phases with different symmetries manifest themselves below T-c. The ultrasound velocity measurements revealed that in CeCoIn5 the Fulde-Ferrel-Larkin-Ovchinikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices, appears at low temperature and high field. The angle resolved magnetothermal transport measurements revealed that in PrOs4Sb12 a novel change in the symmetry of the superconducting gap function occurs deep inside the superconducting state. These results open up a new realm for the study of the superconductivity with multiple phases. (c) 2005 Published by Elsevier Ltd.

DOI： 10.1016/j.jpcs.2005.05.012

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The pressure dependences of the antiferromagnetic and superconducting transition temperatures have been investigated by ac heat capacity measurement under high pressures for the heavy-fermion superconductor CePt3Si without inversion symmetry in the tetragonal structure. The Neel temperature T-N = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure P-AF similar or equal to 0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to about 1.5 GPa. The pressure phase diagram of CePt3Si is thus very unique and has never been reported before for other heavy fermion superconductors.

DOI： 10.1143/JPSJ.74.1903

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Bulk electronic structures of Pr-based filled skutterudites and their reference materials have been investigated by bulk-sensitive photoemission spectroscopy using soft and hard X-rays. For Pr 3d-4f resonance, a strong intensity in the vicinity of Fermi level (EF) is observed only for PrFe4P12. Furthermore, PrFC4P12 has the significant spectral weight of the vertical bar 3d(9)4f(3)> final state in Pr 3d core-level spectrum. We interpret that the observed prominent intensity just below EF arises from a Kondo resonance due to the strong hybridization between the Pr 4f and conduction states. (c) 2005 Elsevier B.V. All Rights Reserved.

DOI： 10.1016/j.elspec.2005.01.025

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The superconducting gap structure of recently discovered heavy fermion CePt3Si without spatial inversion symmetry was investigated by thermal transport measurements down to 40 mK. In zero field a residual T-linear term was clearly resolved as T -> 0, with a magnitude in good agreement with the value expected for a residual normal fluid with a nodal gap structure, together with a T-2 dependence at high temperatures. With an applied magnetic field, the thermal conductivity grows rapidly, in dramatic contrast to fully gapped superconductors, and exhibits one-parameter scaling with T/root(H) over bar. These results place an important constraint on the order parameter symmetry; that is, CePt3Si is most likely to have line nodes.

DOI： 10.1103/PhysRevLett.94.197002

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The pressure dependence of the first-order phase transition (FOPT) at the upper critical field H-c2 in CeCoIn5 has been Studied by magnetization measurements. The FOPT is found to persist at pressures at least up to 1.5 GPa in the c axis and up to 1.38 GPa in the a axis. With increasing pressure, the anisotropy of H-c2 becomes stronger, and the condensation energy decreases significantly. We also observed a notable peak effect near H-c2 under pressure. Our results suggest that the FOPT cannot be accounted for by Pauli limiting alone.

DOI： 10.1143/JPSJ.74.1115

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We report magnetic susceptibility and electrical resistivity measurements under hydrostatic pressure up to 2 GPa on single-crystalline PrCu2, which exhibits the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that the ordered 4f moments lie in the ac plane in the pressure-induced magnetic state. We propose that remarkable pressure effects on the susceptibility and resistivity are due to changes in the quadrupolar state of O-2(2) and/or O-2(0) under pressure. We present a simple analysis in terms of the singlet-singlet model.

DOI： 10.1103/PhysRevB.71.024408

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We report the de Haas-van Alphen (dHvA) effect and magnetoresistance in the filled-skutterudite superconductor LaRu4 P12, which is a reference material of PrRu4 P12 that exhibits a metal-insulator (M-I) transition at TMI 60 K. The observed dHvA branches for the main Fermi surface (FS) are well explained by the band-structure calculation, using the full potential linearized augmented-plane-wave method with the local-density approximation, suggesting a nesting instability with q= (1,0,0) in the main multiply connected FS as expected also in PrRu4 P12. Observed cyclotron effective masses of (2.6-11.8) m0, which are roughly twice the calculated masses, indicate the large mass enhancement even in the La-skutterudites. Comparing the FS between LaRu4 P12 and PrRu4 P12, an essential role of c-f hybridization cooperating with the FS nesting in driving the M-I transition in PrRu4 P12 is clarified. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.132502

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We report evidence for direct CP violation in the decay B-0-->K(+)pi(-) with 253 fb(-1) of data collected with the Belle detector at the KEKB e(+)e(-) collider. Using 275x10(6) B(B) over bar pairs we observe a B-->K(+/-)pi(-/+) signal with 2140+/-53 events. The measured CP violating asymmetry is A(CP)(K(+)pi(-))=-0.101+/-0.025(stat)+/-0.005(syst), corresponding to a significance of 3.9sigma including systematics. We also search for CP violation in the decays B+-->K(+)pi(0) and B+-->pi(+)pi(0). The measured CP violating asymmetries are A(CP)(K(+)pi(0))=0.04+/-0.05(stat)+/-0.02(syst) and A(CP)(pi(+)pi(0))=-0.02+/-0.10(stat)+/-0.01(syst), corresponding to the intervals -0.05< A(CP)(K(+)pi(0))<0.13 and -0.18< A(CP)(pi(+)pi(0))<0.14 at 90% confidence level.

DOI： 10.1103/PhysRevLett.93.191802

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Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure-temperature phase diagram has been investigated by means of the electrical resistivity and magnetization measurements under high pressure. The phase diagram consists of two magnetic phases, the Ising-like ferromagnetic phase (FM1) at low pressures and another magnetic phase (FM2) with the small ferromagnetic component along the [101] direction at high pressures. Superconductivity is observed in the narrow pressure range near the disappearance point of the FM2 phase, where the temperature dependence of resistivity follows the non-Fermi liquid form of T-1.6. From these experimental facts, the superconductivity is considered to be associated with the critical fluctuation with the disappearance of FM2 phase.

DOI： 10.1143/JPSJ.73.3129

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We succeeded in observing de Haas-van Alphen (dHvA) oscillations in an antiferromagnet NpCoGa5 with a tetragonal structure. The dHvA signal was significantly enhanced at higher fields than the metamagnetic transition field H-m (= 43 kOe for H parallel to [001]), where the antiferromagnetic state is changed into the field-induced ferromagnetic (paramagnetic) state. In the paramagnetic state, the Fermi surface was found to consist of two kinds of cylindrical main Fermi surface and small pocket Fermi surfaces. The cyclotron masses of the main Fermi surfaces were considerably large, ranging from 6 to 12 m(0). This is the first case where the Fermi surface was determined experimentally in transuranium compounds.

DOI： 10.1143/JPSJ.73.20608

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DOI： 10.1143/JPSJ.73.2608

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We report high-resolution angle-resolved photoemission spectroscopy of LaRh3B2, which is a nonmagnetic reference compound of RRh3B2 (R: rare-earth metals). We found two hole-like Fermi surfaces (FSs) and two electron-like FSs centered at Gamma(A) and K(H) points, respectively. The estimated volume of FSs at Gamma(A) point shows a good agreement with the LDA band calculation, while the band dispersion and the topology of FSs at K(H) point show a remarkable disagreement. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.06.023

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Electrical resistivity, specific heat, magnetic susceptibility and high-field magnetization measurements have been performed on the ferromagnet UFe4P12 with the cubic crystal structure. The ferromagnetic ordering at T-C = 3.1 K, a small saturation moment of 1.3 mu(B)/U, together with the temperature dependence of the magnetic susceptibility, are found to be well explained by considering the 5f(2) crystalline electric field schemes for T-h site symmetry and the magnetic exchange interaction.

DOI： 10.1143/JPSJ.73.2533

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We measured the electrical resistivity, specific heat, magnetic susceptibility, high-field magnetization, thermal expansion and magnetostriction of an antiferromagnet Ce3Sn7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4f-scheme previously proposed by Bonnet et al. in which the two Cc atoms at the 2(a) site possess a magnetic moment of 0.36 /mu(B)/Ce and the one Ce atom at the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn3. We also constructed the antiferromagnetic phase diagram for the three principal directions. Furthermore, we carried out the de Haas-van Alphen experiment. Fermi surfaces are many in number but extremely small in volumes, indicating that Ce3Sn7 is a semimetal.

DOI： 10.1143/JPSJ.73.2276

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We have grown a single crystal of PrRh3B2 with the hexagonal structure and measured the electrical resistivity, specific heat, de Haas-van Alphen oscillation, magnetic susceptibility, high-field magnetization, thermal expansion and magnetostriction. PrRh3B2 is not a simple ferromagnet as reported previously, but a ferrimagnet with an ordering temperature T-ord = 3.6 K. The Schottky specific heat observed around 25 K and the large anisotropy of the magnetic susceptibility and magnetization are found to be well explained by the crystalline electric field (CEF) with a large overall CEF-splitting energy of 1080 K and a strong ferromagnetic exchange interaction along the [0001] direction. The topology of the Fermi surface in PrRh3B2 is Similar to that of the non-4f reference compound LaRh3B2, exhibiting a quasi-one-dimensional character of the electronic states.

DOI： 10.1143/JPSJ.73.2266

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Ultrasound velocity measurements of the unconventional superconductor CeCoIn5 with extremely large Pauli paramagnetic susceptibility reveal an unusual structural transformation of the flux-line lattice (FLL) in the vicinity of the upper critical field. The transition field coincides with that at which heat capacity measurements reveal a second-order phase transition. The lowering of the sound velocity at the transition is consistent with vortex segmentation and a crossover to quasi-two-dimensional FLL pinning. These results provide strong evidence that the high-field state is the Fulde-Ferrel-Larkin-Ovchinikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices.

DOI： 10.1103/PhysRevB.70.020506

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We succeeded in growing a high-quality NpCoGa5 single crystal by the Ga-flux method and measured its electrical resistivity, specific heat, magnetic susceptibility and magnetization. NpCoGa5 is an antiferromagnet with a Neel temperature of 47 K. The magnetic moment of Np is directed along the [001] direction of a tetragonal crystal structure. A sharp metamagnetic transition was observed at H-m = 43 kOe for H || [001], where the antiferromagnetic state is changed to the paramagnetic state above H-m. The ordered moment was determined to be 0.74 mu(B)/Np. The magnetic properties were discussed on the basis of the crystalline electric field scheme of the 5f(4) configuration.

DOI： 10.1143/JPSJ.73.1665

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We have studied the superconducting property by measuring the electrical resistivity under the magnetic field and pressure for CePt3Si, which is the first antiferromagnetic heavy fermion superconductor without inversion symmetry in its tetragonal crystal structure. The upper critical field H-c2(0) is found to be approximately isotropic: H-c2(0) = 2.7 T for H || [100] and 3.2 T for H || [001]. The Neel temperature T-N = 2.3 K and the zero resistivity superconducting transition temperature T-sc similar or equal to 0.65 K decrease markedly with increasing pressure, suggesting that the present superconductivity is correlated to the anti ferromagnetic state.

DOI： 10.1143/JPSJ.73.1657

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We have studied the magnetic and thermal properties of a single crystal of CePt3Si, which is a recently reported heavy-fermion superconductor with a superconducting transition temperature T-c = 0.75 K and a Neel temperature T-N = 2.2 K. The overall experimental data are principally explained on the basis of the crystalline electric field (CEF) scheme. Even in the antiferromagnetic state, the CEF model applies well to the characteristic features in the magnetization curve. These results indicate the existence of a localized magnetic moment at the Ce site, with a considerably reduced ordered moment of 0.16 mu(B)/Ce, and the strongly correlated conduction electrons are condensed into the superconducting state. We have also constructed the magnetic phase diagram including the superconducting phase for H parallel to [110] and [001].

DOI： 10.1088/0953-8984/16/28/L03

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Ultrasound velocity measurements of the unconventional superconductor CeCoIn5 with extremely, large Pauli paramagnetic susceptibility reveal an unusual structural transformation of the flux-line lattice (FLL) in the vicinity of the upper critical field. The transition field coincides with that at which heat capacity measurements reveal a second-order phase transition. The lowering of the sound velocity at the transition is consistent with vortex segmentation and a crossover to quasi-two-dimensional FLL pinning. These results provide strong evidence that the high-field state is the Fulde-Ferrel-Larkin- Ovchinikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices.

DOI： 10.1103/PhysRevB.70.020506

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We have carried out a de Hass-van Alphen (dHvA) experiment for the recently discovered CePt3Si, which is the first heavy fermion superconductor without inversion symmetry in the tetragonal crystal structure, together with a dHvA experiment for a non-4f reference compound LaPt3Si. As for LaPt3Si, several dHvA branches were observed. Among them, the two main dHvA branches with the dHvA frequency (the cyclotron effective mass) of 1.10 x 10(8) Oe (1.4 m(0)) and 8.41 x 10(7) Oe (1.5 m(0)) were found to be well explained from the FLAPW energy band calculations, corresponding to bands 64- and 63-multiply-connected hole Fermi surfaces, respectively. On the other hand, the dHvA frequencies of 10(7) Oe in CePt3Si are small in magnitude, although the corresponding cyclotron masses of 10-20 m(0) are extremely large.

DOI： 10.1088/0953-8984/16/23/L02

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The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe2. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature T-* where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at T-* at least under high pressure slightly below P-c(*) where T-* becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of C/T is observed in a narrow pressure region (DeltaPsimilar to0.1 GPa) around P-c(*) contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point P-c(*) for the appearance of the superconductivity.

DOI： 10.1103/PhysRevB.69.180513

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We have studied de Hass van Alphen (dHvA) effect under pressure for a pressure-induced superconductor CeRhIn5 and a superconductor CeCoIn5. The topology of the Fermi surface in CeRhIn5 and CeCoIn5 are found to be unchanged up to 2.1 GPa and 3.1 GPa, respectively. On the other hand, the effective mass of CeRhIn5(CeCoIn5) decreases (increases) remarkably with increasing pressure. (C) 2003 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2003.11.087

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We have investigated a change of the electronic state in CeIn3 via de Haas-van Alphen (dHvA) experiments under pressure up to 2.7 GPa. The shape of a spherical Fermi surface with humps along <111> changes slightly at 2.5 GPa. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.200

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We searched for an experimental condition of crystal growth for a ferromagnetic superconductors of UGe2 and URhGe. Samples were prepared for both polycrystalline and single crystals, which were arc-melted and grown by the Czochralski-pulling method in a tetra-arc furnace, respectively. Annealing is an important process to enhance sample-quality, namely the residual resistivity ratio. We tried to anneal the samples under various temperatures, which were wrapped by the Ta-foil and vacuum-sealed in the quartz ample, together with the solid state electrotransport method in ultra-high vacuum. The highest residual resistivity ratio was 900 for UGe2 and 41 for URhGe. (C) 2003 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2003.12.1083

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We report systematic evolution of superconducting (SC) characteristic of heavy-fermion superconductor CeCoIn5 via the nuclear-quadrupole-resonance (NQR) measurement under pressure (P). The temperature dependence of nuclear spin - lattice relaxation rate (1/T-1) below T-C has revealed that once the value of SC energy gap (2 Delta(0)/k(B)T(C)) slightly increases in P<0.45 GPa, with further increasing P, it decreases significantly. By contrast, T-C increases monotonously up to 2.6 K as P increases up to 1 GPa, exhibiting a saturation in P = 1.0-1.5 GPa. (C) 2003 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.335

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In order to characterize the magnetic state at high pressure, anisotropic susceptibilities, chi(a), chi(b) and chi(c) were measured up to 1.8 GPa in PrCu2, which seems to exhibit a pressure-induced Van Vleck paramagent-to-antiferromagnet transition at 1.2 GPa. It is speculated that the ordered 4f-moments lie in the b-plane in the pressure-induced magnetic state. Remarkable pressure-effects on susceptibility are observed in the b-plane, as indicated in the co-operative Jahn-Teller effect and in the metamagnetism under high field. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.078

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We present a study of Nernst and Seebeck coefficients of the heavy-fermion superconductor CeCoIn5. Below 18 K, concomitant with a field-dependent Seebeck coefficient, a large sublinear Nernst signal emerges with a magnitude drastically exceeding what is expected for a multiband Fermi-liquid metal. In the mixed state, in contrast with all other superconductors studied before, this signal overwhelms the one associated with the motion of superconducting vortices. The results point to a hitherto unknown source of transverse thermoelectricity in strongly interacting electrons.

DOI： 10.1103/PhysRevLett.92.217002

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The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe2. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature T* where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at T* at least under high pressure slightly below P*c where T* becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of C/T is observed in a narrow pressure region (ΔP∼0.1 GPa) around P* contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point P*c for the appearance of the superconductivity.

DOI： 10.1103/PhysRevB.69.180513

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We present recent advances in the magnetism and superconductivity of rare earth and uranium compounds. Heavy fermions are formed on the basis of the competition between the RKKY interaction and the Kondo effect in these compounds. The application of pressure to these compounds is useful to control the electronic states in the antiferromagnets CeRh2Si2 and CeRhIn5, and the ferromagnet UGe2. The quadrupole interaction or the quadrupole Kondo effect is found to be responsible for heavy fermions in PrFe4P12. A rich variety of superconducting properties are demonstrated: superconductivity of CeCoIn5 and CeRhIn5 in the vicinity of a quantum critical point, coexistence of ferromagnetism and superconductivity in UGe2, and superconductivity based on the quadrupole fluctuations in PrOs4Sb12, together with the relation between the superconducting transition temperature and the quasi-two dimensionality of the electronic states.

DOI： 10.1143/JPSJ.73.769

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Neutron scattering experiments have been carried out on the heavy fermion antiferromagnetic (AFM) superconductor CePt3Si with T-N = 2.2 K and T-SC = 0.75 K. We observed clear AFM Bragg reflections with Q(0) = (00 1 /2) below and above T-SC, indicating microscopic coexistence of AFM order and heavy fermion superconductivity. The AFM structure, of two interleaved ferromagnetic sublattices of local Ce 4f moments, has inversion symmetry under simultaneous space-time reversal. However, hybridization with Pt and Si breaks this degeneracy and a combination of these two competing effects may be relevant to an understanding of the simultaneous occurrence of superconductivity and AFM order. The observed magnetic moment 0.16(1) mu(B)/Ce is strongly reduced from the Curie-Weiss effective moment 2.54 mu(B)/Ce. Clear crystal field excitations at 1 and 24 meV were observed. The magnetic susceptibility can be well explained in a level scheme assuming the Gamma(7) ground state, Gamma(6) and Gamma(7) first and second excited states, respectively.

DOI： 10.1088/0953-8984/16/15/L01

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We have measured the electrical resistivity, magnetic Susceptibility, high-field magnetization, specific heat and de Haas-van Alphen (dHvA) oscillation of Ce(2)Rhln(8), together with the dHvA oscillation of La2RhIn8. In La2RhIn8 we detected three kinds of dHvA branches showing cylindrical Fermi surfaces, which are well explained by the result Of FLAPW energy band calculations. The corresponding two dHvA branches were detected in Ce2RhIn8, indicating that the topology of the Fermi surface in Ce2RhIn8 is approximately the same as that of LaRhIn8. The magnetic susceptibility and magnetization of Ce2RhIn8 were analyzed on the basis of the crystalline electric field scheme of localized-4f energy levels. Pressure-induced superconductivity was confirmed above 1.2GPa from the resistivity and ac-susceptibility measurements.

DOI： 10.1143/JPSJ.73.649

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We succeeded in observing the de Haas-van Alphen (dHvA) oscillations in NpNiGa5 Single crystals, which were grown by the Ga-flux method. This is the first dHvA observation in transuranium compounds. The cyclotron effective masses were moderately enhanced, ranging from 1.8 to 4.9m(0) (m(0): rest mass of an electron). From an intensive change of the dHvA amplitude at 80-90kOe and the temperature dependence of the electrical resistivity, NpNiGa5 is most likely an antiferromagnet with a Neel temperature, T-N = 30 K.

DOI： 10.1143/JPSJ.73.519

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We report the discovery of pressure-induced superconductivity in ferromagnetic UIr, which lacks inversion symmetry in the crystal structure. The Curie temperature T-CI = 46 K at ambient pressure decreases with increasing pressure, reaching a value of 11 K at 1.5 GPa. It presumably decreases further up to about P-cl = 1.7 GPa. The ferromagnetic region named 'Fl' exists up to P-cl. A second magnetic phase named 'F2' with a low ferromagnetic moment appears in the pressure range frorn 1.9 to 2.4 GPa. In the 'F2' phase, the magnetic transition temperature T-C2 decreases with pressure, from 18 K at 1.9 GPa to approximately zero at P-C2 = 2.6-2.7 GPa. In this critical pressure region, superconductivity appears below T-sc = 0.14 K.

DOI： 10.1088/0953-8984/16/4/L02

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The normal-state Hall effect and magnetoresisitance (MR) have been measured in the quasi two dimensional (2D) heavy fermion superconductor CeCoIn5. In the non-Fermi liquid region where the reistivity rho(xx) exhibits an almost perfect T-linear dependence, the Hall angle varies as cot theta(H) proportional to T-2 and MR displays a strong violation of Kohler's rule. We demonstrate a novel relation between the MR and the Hall conductivity, Deltarho(xx)/rho(xx) proportional to (sigma(xy)rho(xx))(2). These results bear a striking resemblance to the normal-state properties of high-T-c cuprates, indicating universal transport properties in the presence of quasi-2D anti ferromagnetic fluctuations near a quantum critical point.

DOI： 10.1143/JPSJ.73.5

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Field-angle-dependent specific heat measurements have been made on the heavy-fermion superconductor CeCoIn5 down to similar to0.29 K, in a magnetic field rotating in the tetragonal c-plane. A clear fourfold angular oscillation is observed in the specific heat with the minima (maxima) occurring along the [100] ([110]) directions. Oscillation persists down to low fields H much less than H-c2, thus directly proving the existence of gap nodes. The results indicate that the superconducting gap symmetry is most probably of d(xy) type.

DOI： 10.1088/0953-8984/16/3/L02

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We have carried out de Haas-van Alphen (dHvA) experiments on a ferromagnet CeRh3B2 with an extremely high Curie temperature T-C similar or equal to 120 K and a non-4f reference compound LaRh3B2. The dHvA data of LaRh3B2 are well explained by the results of energy band calculations. The topology of the Fermi surfaces in CeRh3B2 is found to be very similar to that of LaRh3B2, possessing wavy but flat Fermi surfaces in the basal plane. Observation of a quasi-one-dimensional electronic state is the first such case in a rare earth compound.

DOI： 10.1088/0953-8984/15/46/L02

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DOI： 10.1143/JPSJ.72.2692

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A series of the ternary compounds CeTBi2 (T: Ni, Cu and Ag) have been grown in the single crystalline form by means of the flux method. These compounds crystallize in the tetragonal crystal structure. Measurements of the electrical resistivity, magnetic susceptibility, magnetization, low temperature specific heat and de Haas-van Alphen effect are reported. These compounds order antiferromagnetically with an easy-axis of magnetization along the [001] direction(c-axis). The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the quasi-two dimensional crystal structure.

DOI： 10.1143/JPSJ.72.2632

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We have succeeded in growing a single crystal of CePtGe2 with the orthorhombic crystal structure by the Bi-flux method. In order to investigate the anisotropic properties, the magnetic susceptibility, magnetization and electrical resistivity measurements have been performed along the principal axes. From these measurements, it is found that CePtGe2 orders ferromagnetically below T-C = 5.1 K, and the magnetic easy-axis corresponds to the a-axis. The anisotropic properties have been analyzed on the basis of the crystalline electric field model. We have also studied the pressure effect on the ferromagnetic ordering, and T-C is found to increase with increasing pressure. However, T-C smears out around 3.5 GPa and a new phase appears at higher pressures, where the transition temperature of the new phase also increases with increasing pressure.

DOI： 10.1143/JPSJ.72.2338

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We report In-NQR and Co-NMR experiments of CeCoIn5 that undergoes a superconducting transition with a record high T-c = 2.3 K to date among heavy-fermion superconductors. At zero magnetic field, an anomalous temperature (T) dependence of nuclear spin-lattice relaxation rate 1/T-1 of In-115 is explained by the relation 1/T-1 proportional to T (.) chi(Q)(T)(3/4) based on the anisotropic spin-fluctuations model in case of the proximity to an antiferromagnetic (AFM) quantum critical point (QCP). The novel behavior of 1/T-1 similar to T-1/4 over a wide T range of T-c < T < 40 K arises because the staggered susceptibility almost follows the Curie law chi(Q)(T) proportional to 1/(T + theta) with theta = 0.6 K and hence 1/T-1 proportional to T/(T + 0.6)(3/4) similar to T-1/4 for theta < T. We highlight that the behavior 1/T-1 similar to T-1/4 is due to the proximity to the anisotropic AFM QCP relevant with. its layered structure, and is not associated with the AFM QCP for isotropic 3D systems. We have also found that the AFM spin fluctuations in CeCoIn5 are suppressed by small magnetic field so that theta = 0.6 K at H = 0 increases to theta = 2.5 K at H = 1.1 T, reinforcing that CeCoIn5 is closely located at the QCP.

DOI： 10.1143/JPSJ.72.2308

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We have carried out a de Haas-van Alphen experiment under pressure on a heavy-fermion superconductor, CeCoIn5. Large cyclotron masses of 15 m(0) (m(0:) the rest mass of an electron) in a nearly cylindrical Fermi surface called alpha(i) (i = 1, 2, 3) and 60 m(0) in a similar cylindrical Fermi surface called beta(2) at ambient pressure are found to be strongly reduced to 7 and 40 m(0), respectively, at 3 GPa. Correspondingly, the field-dependent cyclotron mass at ambient pressure becomes almost independent of the field at high pressures. These results indicate that CeCoIn5, which is in the vicinity of the quantum critical region at ambient pressure, is changed into a usual heavy-fermion state under high pressures of about 3 GPa.

DOI： 10.1088/0953-8984/15/32/101

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In order to understand the anisotropic magnetic and electrical properties of ternary compounds CeTSb2 (T=Cu, Au, Ni) with the tetragonal structure, we have grown single crystals of this series by the self-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat. CeCuSb2 and CeAuSb2 are found to order antiferromagnetically with Neel temperatures of 6.9 K and 5.0 K, respectively, while CeNiSb2 is a ferromagnet with a Curie temperature of 6.0 K with an easy axis of magnetization oriented along the [100] direction. The magnetic property of CeCuSb2 shows a very small anisotropy, whereas the electrical resistivity is highly anisotropic between Jparallel to [100] and [001]. In contrast, CeAuSb2 and CeNiSb2 show a strong anisotropy both in the magnetic and electrical measurements, although the magnetic easy axis is interchanged with respect to each other. The anisotropy in the magnetic properties has been explained on the basis of a crystalline electric-field model.

DOI： 10.1103/PhysRevB.68.054427

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We have measured the electrical resistivity under pressure up to 2 GPa for an antiferromagnet, CeRhGe. The resistivity at ambient pressure decreases monotonically below a Neel temperature T-N = 10 K. With increasing pressure P, the resistivity has a peak around 10 K, which is anomalously enhanced up to 1.2 GPa. With further increasing pressure, the resistivity peak is diminished; the Neel temperature becomes zero at a critical pressure P-c = 9 GPa. The A-value of the resistivity rho in the Fermi liquid relation rho = rho(0) +AT(2) is also found to increase with increasing pressure and has a maximum at Pc which corresponds to the value for the heavy-fermion superconductor CeCu2Si2.

DOI： 10.1088/0953-8984/15/29/102

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We report the pressure effects on lattice constants, magnetic susceptibility, specific heat and electrical resistivity in the orthorhombic PrCu2. Anisotropic compression is realized to be kappa(a) approximate to kappa(c) < kappa(b) even under hydrostatic pressure. Above 1.2 GPa, susceptibility shows a remarkable maximum at T-max. This fact implies that the pressure-induced magnetic ordering occurs above 1.2 GPa. Also the results of specific heat and electrical resistivity reveal the anomaly at P = 1.2 GPa to be due to an antiferromagnetic ordering. The temperature-pressure phase diagram is presented up to 2 GPa.

DOI： 10.1143/JPSJ.72.1758

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The exotic features of the Pr-based filled skutterudites are reviewed based on the electronic transport properties, specific heat and de Haas-van Alphen experiments, putting the emphasis on PrFe4P12 and PrOs4Sb12. As references, the experiments on the related La- and Ce-filled skutterudites are also examined and discussed. Compared to their La reference compounds, the Fermi surface is very similar in PrOs4Sb12, suggesting the well localized character of 4f electrons, while it looks largely different in PrFe4P12. For the cyclotron effective mass, both PrFe4P12 and PrOS4Sb12 exhibit a strong enhancement, in reasonable agreement with the large specific heat coefficient.

DOI： 10.1088/0953-8984/15/28/326

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We carried out a de Haas-van Alphen (dHvA) experiment under pressure on a heavy-fermion superconductor, URu2Si2. The dHvA frequency, which corresponds to a nearly spherical Fermi surface, increases slightly with increasing pressure, while the corresponding cyclotron mass decreases considerably. Neither the dHvA frequency nor the cyclotron mass exhibit any abrupt change at the critical pressure of 1.5 GPa. The present result is thus inconsistent with a recent phase-separation proposal.

DOI： 10.1088/0953-8984/15/28/316

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We studied the electronic states of two antiferromagnets, UPtGa5 and UN, by measuring the electrical resistivity under pressure. When pressure P is applied, the Neel temperature T-N decreases, becoming zero at P-c = 8.0 GPa for UPtGa5 and P-c = 3.5 GPa for UN.

DOI： 10.1088/0953-8984/15/28/315

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We present descriptions of the single crystal growth of uranium and cerium compounds via the Czochralski-pulling, self-flux and vapour transport methods. We also report the results of de Haas-van Alphen experiments and energy band calculations for a Hill-plot rule of UX3 (X: Si, Ge, Sn and Pb), heavy fermion systems of UPt3 and UPd2Al3, quasi-two-dimensional electronic states of UPtGa5, UX2 (X: Bi, Sb, As, P) and CeCoIn5, characteristic semimetals of UC and CeAgSb2, and quantum critical phenomena in UGe2 and CeRh2Si2.

DOI： 10.1088/0953-8984/15/28/301

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We measured the magnetization of CeCu2, PrCu2, TbCu2, DyCu2 and TmCu2 in high magnetic fields up to 40 T and in a wide temperature range from 1.3 to 150 K, and observed a metamagnetic transition with a large hysteresis. The present metamagnetic transition occurs in the ac-plane of the orthorhombic crystal structure, which was analysed on the basis of the quadrupole moment O-2(2). (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(03)00069-6

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When pressure is applied to cerium and uranium compounds, the magnetic ordering temperature is suppressed and becomes zero at a critical pressure P-c. Around P-c, non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via a de Haas-van Alphen (dHvA) experiment when pressure crosses P-c. The dHvA experiment under pressure was done for the antiferromagnets CeRh2Si2 and CeRhIn5, and for a ferromagnet UGe2. We found an abrupt change of the Fermi surface for CeRh2Si2 and UGe2 when crossing P-c, indicating a first-order like phase transition. For CeRhIn5, the topology of the Fermi surface was unchanged, but the cyclotron mass increased steeply above 1.6 Gpa, where superconductivity sets in. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(03)00070-2

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We have studied the de Haas-van Alphen (dHvA) effect under pressure for an antiferromagnet CeRhIn5, where the antiferromagnetic state is changed into the superconducting state at higher pressures than 1.6 GPa. It is clarified from the present dHvA experiment that the topology of the Fermi surface is unchanged up to 2.1 GPa but the cyclotron mass increases strongly above 1.6 GPa. Superconductivity is found to be realized in this heavy fermion state. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02366-9

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We performed the heat capacity, C(T), measurement under high pressure on a ferromagnetic superconductor UGe2, in order to study the pressure dependence of the anomaly in C(T) associated with the superconducting transition. A clear peak appears only around a critical pressure P-c(*) where an another transition temperature T* becomes 0 K. This result suggests that a bulk superconducting phase exists in the narrower pressure region around P-c(*), than those clarified by previous studies. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02650-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We report evidences for bulk nature and unconventional superconductivity in CeIn3 at P = 2.65 GPa revealed by the measurements of nuclear-spin-lattice-relaxation time (T-1) and ac-susceptibility (ac-chi). Both the measurements of ac-chi and T, have pointed to a superconducting transition at T = 95 mK, which is very much lower than an onset temperature T-onset = 0.15 K at zero resistance. The temperature dependence of 1/T-1 shows no coherence peak just below T-c, indicative of an unconventional nature for the superconductivity. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02732-6