Faculty Profiles - SETTAI Rikio

Papers - SETTAI Rikio

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Huge residual resistivity in the quantum critical region of CeAgSb2 Reviewed

M Nakashima, S Kirita, R Asai, TC Kobayashi, T Okubo, M Yamada, A Thamizhavel, Y Inada, R Settai, A Galatanu, E Yamamoto, T Ebihara, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 15 ( 4 ) L111 - L117 2003.2

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

We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb2 which has a small net ferromagnetic moment of 0.4 mu(B)/Ce. The magnetic ordering temperature. T-ord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure p(c) similar or equal to 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55 muOmega cm at p(c). A huge residual resistivity is found to appear when the magnetic order disappears.

DOI： 10.1088/0953-8984/15/4/101

de Haas-van Alphen experiments under pressure in UGe2 Reviewed

R Settai, M Nakashima, H Shishido, Y Haga, H Yamagami, Y Onuki

ACTA PHYSICA POLONICA B 34 ( 2 ) 725 - 728 2003.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS

We have studied the electronic state in UGe2 via the de Haas-van Alphen effect under pressure. The cyclotron masses are determined in the strongly polarized phase and in the paramagnetic phase for magnetic field along the c-axis and the results are compared with those along a- and b-axes.

Superconductivity in CeRh2Si2 under pressure Reviewed

S Araki, M Nakashima, R Settai, TC Kobayashi, Y Onuki

ACTA PHYSICA POLONICA B 34 ( 2 ) 439 - 442 2003.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS

We have studied the pressure-induced superconductivity in an antiferromagnet CeRh2Si2 by measuring the electrical resistivity for a high-quality single crystal. The superconducting resistivity drop was observed around P-c similar or equal to 1.06 GPa, at which the Neel temperature becomes zero(1) namely in a pressure region from 0.97 to 1.20 GPa. The zero resistivity appears below 0.4 K between 1.03 to 1.08 GPa. The resistivity at low temperatures follows the Fermi liquid AT(2) relation in the whole pressure region, even at P-c. The A value becomes a maximum around P-c.

First-order superconducting transition at the upper critical field in CeCoIn5 studied by DC magnetization measurement Reviewed

T Sakakibara, T Tayama, A Harita, Y Haga, H Shishido, R Settai, Y Onuki

ACTA PHYSICA POLONICA B 34 ( 2 ) 467 - 470 2003.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS

DC magnetization process of a high-quality single crystal of CeCoIn5 has been measured at low temperatures down to 50mK. A sharp magnetization jump with a small hysteresis is observed at the upper critical field H-c2 for both a and c directions, indicating the transition to the normal state to be of first-order. Although the results might suggest a strong Pauli paramagnetic effect, no Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase is observed.

A heat capacity anomaly at T* in a ferromagnetic superconductor UGe2 Reviewed

N Tateiwa, TC Kobayashi, K Amaya, Y Haga, R Settai, Y Onuki

ACTA PHYSICA POLONICA B 34 ( 2 ) 515 - 518 2003.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS

We performed the heat capacity, C(T), measurement under high pressure for a ferromagnetic superconductor UGe2. At 1.15 GPa, we found a peak in C/T at a characteristic temperature, T-* = 6 K where the magnetization showed anomalous increase. At 1.28 GPa, above the critical pressure P-c(*) where T-* becomes 0 K, C/T does not show notable anomaly at zero magnetic field, but the application of the external field above 2.5 T induces the peak again at T-* > 0 K. It corresponds to the induction of T-* by the magnetic field. Our experimental result suggests that a second order phase transition takes place at T-* and thus a disappearance of the phase transition at T-* is of second order.

Single crystal growth and annealing temperature of ferromagnetic URhGe Reviewed

E Yamamoto, Y Haga, TD Matsuda, Y Inada, R Settai, Y Tokiwa, Y Onuki

ACTA PHYSICA POLONICA B 34 ( 2 ) 1059 - 1062 2003.2

Language：English Publishing type：Research paper (scientific journal) Publisher：JAGIELLONIAN UNIV PRESS

We searched for an experimental condition of crystal growth for a ferromagnetic superconductor URhGe. Samples were prepared for both poly-crystalline 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 in order to increase 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 (SSE) method in ultra-high vacuum.

Magnetic Properties of CeRhIn5 under Pressure Probed by 115In-NQR

S. Kawasaki, T. Mito, G.-q. Zheng, Y. Kawasaki, Y. Kitaoka, D. Aoki, Y. Haga, R. Settai, Y. Onuki

Acta Phys. Polonica B 2003

Evolution of pressure-induced heavy fermion state and superconductivity in CeRhIn5: A high-pressure fermi surface study

H. Shishido, R. Settai, S. Araki, T. Ueda, Y. Inada, T. C. Kobayashi, T. Muramatsu, Y. Haga, Y. Onuki

Physical Review B - Condensed Matter and Materials Physics 66 ( 21 ) 2145101 - 2145105 2002.12

Language：English Publishing type：Research paper (scientific journal)

Evolution of the pressure-induced heavy fermion state and superconductivity in CeRhIn5 have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch β2 increases from 5.5 m0 at ambient pressure to 20 m0 at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 m0 at 2.1 GPa, with a concomitant increase of the superconducting transition temperature. However, the underlying Fermi surface remains approximately same even at 2.1 GPa, strongly suggesting that antiferromagnetic fluctuations of Ce moments do not contribute to the volume of the Fermi surface, but enhance the cyclotron mass of the conduction electrons.

Fermi surface of the heavy-fermion superconductor PrOs4Sb12

H. Sugawara, S. Osaki, S. R. Saha, Y. Aoki, H. Sato, Y. Inada, H. Shishido, R. Settai, Y. Onuki, H. Harima, K. Oikawa

Physical Review B - Condensed Matter and Materials Physics 66 ( 22 ) 2205041 - 2205044 2002.12

Language：English Publishing type：Research paper (scientific journal)

We have investigated the de Haas-van Alphen effect in the Pr-based heavy-fermion superconductor PrOs4Sb12. The topology of Fermi surface is close to the reference compound LaOs4Sb12 and well explained by the band-structure calculation based on the FLAPW (full potential linearized augmented-plane-wave)-LDA (local-density approximation) + U method, where the 4f electrons are localized. We have confirmed a highly enhanced cyclotron effective mass (2.4-7.6)m0, which is apparently large compared to the usual Pr-based compounds.

Fermi surface of the heavy-fermion superconductor PrOs4Sb12 Reviewed

H Sugawara, S Osaki, Saha, SR, Y Aoki, H Sato, Y Inada, H Shishido, R Settai, Y Onuki, H Harima, K Oikawa

PHYSICAL REVIEW B 66 ( 22 ) 2002.12

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

We have investigated the de Haas-van Alphen effect in the Pr-based heavy-fermion superconductor PrOs4Sb12. The topology of Fermi surface is close to the reference compound LaOs4Sb12 and well explained by the band-structure calculation based on the FLAPW (full potential linearized augmented-plane-wave)-LDA (local-density approximation) +U method, where the 4f electrons are localized. We have confirmed a highly enhanced cyclotron effective mass (2.4-7.6)m(0), which is apparently large compared to the usual Pr-based compounds.

DOI： 10.1103/PhysRevB.66.220504

An unusual hollow cylindrical Fermi surface of a quasi-two-dimensional compound CeAgSb2 Reviewed

Y Inada, A Thamizhavel, H Yamagami, T Takeuchi, Y Sawai, S Ikeda, H Shishido, T Okubo, M Yamada, K Sugiyama, N Nakamura, T Yamamoto, K Kindo, T Ebihara, A Galatanu, E Yamamoto, R Settai, Y Onuki

PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES 82 ( 18 ) 1867 - 1892 2002.12

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

We have carried out the de Haas-van Alphen (dHvA) experiment, together with electrical resistivity, magnetic susceptibility, magnetization and specific heat experiments on a high-quality single-crystal CcAgSb(2), which has a small net ferromagnetic moment of 0.4 mu(B) per Cc atom. The bulk magnetic properties are well explained by the crystalline electric field scheme. On the other hand, large dHvA frequencies of 10(8) Oe, which correspond to cylindrical Fermi surfaces, were detected by the dHvA measurement for the magnetic field along the tetragonal [001] direction, indicating the quasi-two-dimensional electronic structure. The dHvA branches of CeAgSb2 are highly different from those with small dHvA frequencies of 10(7) Oe for the reference compounds LaAgSb2 and YAgSb2 which exhibit a semimetallic character. The dHvA results have been compared with the results of the energy band calculations. It was concluded that the 4f electron is mainly localized and that the Fermi surface of CeAgSb2 is similar to that of LaAgSb2, but it is slightly enlarged so as to form the large orbits along a hollow cylindrical Fermi surface.

DOI： 10.1080/1364281021000036823

Pressure-induced superconductivity in a ferromagnet, UGe2: resistivity measurements in a magnetic field Reviewed

TC Kobayashi, K Hanazono, N Tateiwa, K Amaya, Y Haga, R Settai, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 44 ) 10779 - 10782 2002.11

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

Electrical resistivity measurements in a magnetic field are carried out on UGe2 which exhibits pressure-induced superconductivity. The superconductivity is observed from 1.06 to 1.44 GPa. In the temperature and field dependences of the resistivity at P > PC where the ferromagnetic ordering disappears, it is observed that the application of an external field along the a-axis increases the coefficient A of the Fermi-liquid behaviour (alphaAT(2)) abruptly-corresponding to the metamagnetic transition. The characteristic enhancement of H-C2 is reconfirmed for H parallel to a-axis. The upper critical field of H-C2 is anisotropic: H-C2(T) exhibits positive curvature for H parallel to b-axis and H parallel to c-axis.

DOI： 10.1088/0953-8984/14/44/376

Exotic heavy-fermion state in the filled skutterudite PrFe4P12 uncovered by the de Haas-van Alphen effect

H. Sugawara, T. D. Matsuda, K. Abe, Y. Aoki, H. Sato, S. Nojiri, Y. Inada, R. Settai, Y. Onuki, Y. Onuki

Physical Review B - Condensed Matter and Materials Physics 66 1344111 - 1344115 2002.10

We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe4P12 exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass mc* = 81 m0 in the high field phase, which indicates that PrFe4P12 is the first Pr compound in which really heavy mass has been unambiguously confirmed. Also in the low field nonmagnetic ordered phase (LOP), we observed the dHvA branch with mc* = 10 m0 that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

Exotic heavy-fermion state in the filled skutterudite PrFe4P12 uncovered by the de Haas-van Alphen effect Reviewed

H Sugawara, TD Matsuda, K Abe, Y Aoki, H Sato, S Nojiri, Y Inada, R Settai, Y Onuki

PHYSICAL REVIEW B 66 ( 13 ) 2002.10

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

We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe4P12 exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass m(c)(*)=81 m(0) in the high field phase, which indicates that PrFe4P12 is the first Pr compound in which really heavy mass has been unambiguously confirmed. Also in the low field nonmagnetic ordered phase (LOP), we observed the dHvA branch with m(c)(*)=10 m(0) that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

DOI： 10.1103/PhysRevB.66.134411

In-115-NQR evidence for unconventional superconductivity in CeIn3 under pressure Reviewed

S Kawasaki, T Mito, Y Kawasaki, GQ Zheng, Y Kitaoka, H Shishido, S Araki, R Settai, Y Onuki

PHYSICAL REVIEW B 66 ( 5 ) 2002.8

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

We report evidence for unconventional superconductivity in CeIn3 at a pressure P=2.65 GPa above the critical pressure (P(c)similar to2.5 GPa) revealed by measurements of the nuclear-spin-lattice-relaxation time (T-1) and ac susceptibility (ac-chi). Both measurements of T-1 and ac-chi have pointed to a superconducting transition at T-c=95 mK, which is much lower than the 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 induced in CeIn3.

DOI： 10.1103/PhysRevB.66.054521

Magnetization study of the heavy fermion superconductor CeCoIn5 Reviewed

T Tayama, A Harita, T Sakakibara, Y Haga, H Shishido, R Settai, Y Onuki

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1155 - 1158 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We report the high-resolution dc magnetization measurements in the heavy fermion superconductor CeCoIn5 at very low temperatures down to 50 mK in fields up to 125 kOe. A clear magnetization jump is observed at the upper critical field H,2 for both Hparallel toa and c axes in the isothermal magnetization curve below 0.7 K, indicating the existence of a first-order phase transition at H-c2, It is likely that the first-order phase transition is ascribed to a strong Pauli paramagnetic suppression in the even-parity pairing. In the normal state above H,2 we found non-Fermi liquid behavior in the temperature dependence of the magnetization down to 150 mK, suggesting the presence of antiferromagnetic fluctuations. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00008-2

Heavy fermions in cerium and uranium compounds studied by the de Haas-van Alphen experiment Reviewed

S Araki, R Settai, M Nakashima, H Shishido, S Ikeda, H Nakawaki, Y Haga, N Tateiwa, TC Kobayashi, H Harima, H Yamagami, Y Aoki, T Namiki, H Sato, Y Onuki

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1133 - 1139 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We carried out the de Haas-van Alphen (dHvA) experiment under pressure to clarify the nature of f-electron compounds of CeRh2Si2, UGe2 and CeCoIn5. With increasing pressure, the Neel temperature T-N = 36 K in CeRh2Si2 and the Curie temperature T-C = 52 K in UGe2 decrease, and a quantum critical point corresponding to the extrapolation T-N or T-C --> 0 is reached at the critical pressure p(c) similar or equal to 1.06 and 1.52 GPa, respectively. Experimental results indicate a discontinuous change of the Fermi surface in CeRh2Si2 and UGe2 when the pressure crosses pc. A heavy fermion superconductor CeCoIn5 with a quasi-two dimensional Fermi surface was found to be located in the vicinity of the quantum critical point. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00156-7

Coexistence of antiferromagnetism and superconductivity in heavy-fermion systems Reviewed

Y Kitaoka, Y Kawasaki, T Mito, S Kawasaki, GQ Zheng, K Ishida, D Aoki, Y Haga, R Settai, Y Onuki, C Geibel, F Steglich

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1141 - 1146 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We report the novel pressure (P)-temperature (T) phase diagrams of antiferromagnetism (AFM) and superconductivity (SC) in CeRhIn5, CeIn3, and CeCu2Si2 revealed by the nuclear quadrupole resonance measurement. In the itinerant helical magnet CeRhIn5, we found that the Neel temperature T-N is reduced at P greater than or equal to 1.23 GPa with an emergent pseudogap behavior. The coexistence of AFM and SC is found in a narrow P range of 1.63-1.75 GPa, followed by the onset of SC with line-node gap over a wide P window 2.1-5 GPa. In CeIn3, the localized magnetic character is robust against the application of pressure up to P similar to 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations. In CeCu2Si2, the SC and AFM coexist on a microscopic level once its lattice parameter is expanded. We remark that the underlying marginal AFM state is due to collective magnetic excitations in the superconducting state in CeCu2Si2. An interplay between AFM and SC is discussed on the SO(5) scenario that unifies AFM and SC. We suggest that the SC and AFM in CeCu2Si2 have a common mechanism. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00133-6

Probing the nodal structure in quasi-2D unconventional superconductors by thermal conductivity Reviewed

K Izawa, H Yamaguchi, Y Matsuda, T Sasaki, R Settai, Y Onuki

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1055 - 1059 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

The superconducting gap structure is an unresolved issue in most of unconventional superconductors. Here we measured the thermal conductivity of 2D unconventional superconductors, spin-triplet Sr2RuO4, heavy fermion CeCoIn5 and organic kappa-(BEDT-TTF)(2)Cu(NCS)(2), in magnetic field rotating within the 2D planes. On the basis of the angular variation in the thermal conductivity, we demonstrate that the gap function is d(k) = Delta(0)(z) over cap (k(x) + ik(y))(cos ck(z) + alpha) for Sr2RuO4, d(x2-y2) for CeCoIn5, and d(xy). for kappa-(BEDT-TTF)(2)Cu(NCS)(2). (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00134-8

Pressure-induced superconductivity in an antiferromagnet CeRh2Si2 Reviewed

S Araki, M Nakashima, R Settai, TC Kobayashi, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 21 ) L377 - L383 2002.6

Language：English Publisher：IOP PUBLISHING LTD

We studied the pressure effect by measuring the electrical resistivity for a high-quality single crystal of an antiferromagnet CeRh2Si2 with the tetragonal structure. The Neel temperature becomes zero around I GPa. An onset of superconductivity appears below 0.5 K in a relatively wide pressure region from 0.97 to 1.20 GPa, while the resistivity zero, which appears below 0.4 K, is found to be located in an extremely narrow region from 1.03 to 1.08 GPa. Correspondingly the A value of the Fermi liquid relation in the electrical resistivity (rho = rho(0) + AT(2)) becomes maximum around I GPa. Superconductivity is realized in a heavy fermion state.

DOI： 10.1088/0953-8984/14/21/102

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