Faculty Profiles - KOBAYASHI Tatsuo

Papers - KOBAYASHI Tatsuo

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De Haas-Van Alphen experiments under extreme conditions of low temperature, high field and high pressure, for high-quality cerium and uranium compounds Reviewed

R Settai, S Araki, H Shishido, Y Inada, Y Haga, E Yamamoto, TC Kobayashi, N Tateiwa, Y Onuki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 262 ( 3 ) 399 - 406 2003.6

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

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

Magnetic ordering in the pressure-stabilized high-temperature phase of YbInCu4 Reviewed

T Mito, T Koyama, M Shimoide, S Wada, T Muramatsu, TC Kobayashi, JL Sarrao

PHYSICAL REVIEW B 67 ( 22 ) 2003.6

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

To elucidate the ground state of the pressure-stabilized high-temperature (HT) phase of YbInCu4, we have carried out electrical resistivity rho and ac-susceptibility chi(ac) measurements at high pressures. For pressures above 2.49 GPa, the first-order valence transition is completely suppressed (below similar to80 mK). Separately, above 2.39 GPa, a clear peak appears in chi(ac) with a small kink in rho at around T-M=2.4 K. The chi(ac) peak is easily diminished by applying low magnetic fields and disappears above similar to500 Oe. The characteristic behavior of chi(ac) at T-M can generally be ascribed to the onset of long-range ferromagnetic ordering and, therefore, the ground state of the pressure-stabilized HT phase is most probably a ferromagnetically ordered state. This result is compatible with the occurrence of weak ferromagnetism recently reported for the Y-substituted compound Yb0.8Y0.2InCu4 under pressure of 1.2 GPa.

DOI： 10.1103/PhysRevB.67.224409

A heat capacity anomaly of the superconducting transition in a ferromagnetic superconductor UGe2 Reviewed

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

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 527 - 528 2003.5

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

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

Specific heat of an S=1 quasi-1D bond alternating antiferromagnet in a magnetic field Reviewed

N Tateiwa, M Hagiwara, H Aruga-Katori, TC Kobayashi

PHYSICA B-CONDENSED MATTER 329 1209 - 1210 2003.5

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

We report the results of specific heat measurements in a magnetic field on single crystal samples of the S = 1 quasi-1D bond alternating antiferromagnet Ni(C9H24N4)NO2(ClO4). The compound has the singlet ground state with an excitation energy gap and the gap closes by application of magnetic field (H-c). We observed a sharp peak corresponding to the long-range ordering above Hc both parallel and perpendicular to the chain at low temperatures. The temperature-magnetic field phase diagram is discussed in comparison with those of the Haldane system Ni(C5H14N2)(2)N-3(PF6). (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02130-0

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.

De Haas-van Alphen experiments in the quantum critical region of cerium and uranium compounds Reviewed

Y Onuki, R Settai, S Araki, M Nakashima, H Ohkuni, H Shishido, A Thamizhavel, Y Inada, Y Haga, E Yamamoto, TC Kobayashi

ACTA PHYSICA POLONICA B 34 ( 2 ) 667 - 678 2003.2

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

When pressure is applied to the cerium and uranium compounds, their magnetic ordering temperatures are suppressed and become 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 the de Haas-van Alphen (dHvA) experiment when pressure crosses P-c. The dHvA experiment under pressure was done for antiferromagnets CeRh2Si2, CeRhIn5 and URu2Si2, and a ferromagnet UGe2. We find an abrupt change of the Fermi surface for CeRh2Si2 and UGe2 when crossing P-c, indicating a first-order like phase transition. For CeRhIn5 and URu2Si2, a change of the cyclotron mass is clearly observed.

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

Electrical resistivity of CeTIn5 (T=Rh, Ir) under high pressure Reviewed

T. Muramatsu, T. C. Kobayashi, K. Shimizu, K. Amaya, D. Aoki, Y. Haga, Y. Onuki

Physica C 2003

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

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.

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

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

PHYSICAL REVIEW B 66 ( 21 ) 2002.12

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

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 beta(2) increases from 5.5 m(0) at ambient pressure to 20 m(0) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 m(0) 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.

DOI： 10.1103/PhysRevB.66.214510

Formation of a one-dimensional array of oxygen in a microporous metal-organic solid Reviewed

R Kitaura, S Kitagawa, Y Kubota, TC Kobayashi, K Kindo, Y Mita, A Matsuo, M Kobayashi, HC Chang, TC Ozawa, M Suzuki, M Sakata, M Takata

SCIENCE 298 ( 5602 ) 2358 - 2361 2002.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER ASSOC ADVANCEMENT SCIENCE

We report the direct observation of dioxygen molecules physisorbed in the nanochannels of a microporous copper coordination polymer by the MEM (maximum entropy method)/Rietveld method, using in situ high-resolution synchrotron x-ray powder diffraction measurements. The obtained MEM electron density revealed that van der Waals dimers of physisorbed O(2) locate in the middle of nanochannels and form a one-dimensional ladder structure aligned to the host channel structure. The observed O-O stretching Raman band and magnetic susceptibilities are characteristic of the confined O(2) molecules in one-dimensional nanochannels of CPL-1 (coordination polymer 1 with pillared layer structure).

DOI： 10.1126/science.1078481

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： 10.1088/0953-8984/13/1/103

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

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

Pressure study of an antiferromagnet, CeMg2Cu9 Reviewed

H Nakawaki, Y Inada, R Asai, M Yamada, T Okubo, S Ikeda, A Thamizhavel, TC Kobayashi, R Settai, E Yamamoto, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 14 ) L305 - L311 2002.4

Language：English Publisher：IOP PUBLISHING LTD

We have studied the effect of pressure on the electrical resistivity of the antiferrornagnet CeMg2Cu9 which crystallizes in the hexagonal structure. The structure is built up of alternating MgCu2 Laves-type and CeCu5-type layers along the [0001] direction. The Neel temperature T-N = 2.7 K at ambient pressure decreases with increasing pressure p and disappears at a critical pressure p(e) similar or equal to 2.5 GPa. Correspondingly, the residual resistivity rho(0) and the coefficient A in a Fermi-liquid relation rho = rho(0) + AT(2) are found to have maximum values around p(e).

DOI： 10.1088/0953-8984/14/14/101

Heat capacity of the pressure-induced superconductivity in itinerant ferromagnet UGe2 Reviewed

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

PHYSICA B-CONDENSED MATTER 312 109 - 111 2002.3

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

Recently, co-existence of the ferromagnetism and superconductivity was reported in the high-pressure region (1.0-1.6 GPa) in UGe2. We performed the heat capacity measurement on UGe2 under high pressure. At 1.15 GPa, we found a peak corresponding to the superconducting transition. The superconducting temperature T-sc and DeltaC/(gammaTSC) are 0.6 K and 0.25, respectively. The superconducting transition was also confirmed by the appearance of the Meissner effect in the AC susceptibility. From these results, we confirm a bulk nature of the superconductivity in UGe2. The value of C/T (similar to 95 mJ/molK(2)) just above Tsc at 1.15 GPa is as much as 3 times larger than that at ambient pressure, which indicates a large mass enhancement of quasiparticles under high pressure. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01076-6

Transport properties of CeRhIn5 under high pressures up to 8.5 GPa Reviewed

T Muramatsu, N Tateiwa, TC Kobayashi, K Shimizu, K Amaya, D Aoki, H Shishido, Y Haga, Y Onuki

PHYSICA B-CONDENSED MATTER 312 140 - 141 2002.3

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

Transport properties of a pressure-induced superconductor CeRhIn5 were investigated under high pressures up to 8.5 GPa by using a diamond-anvil cell. Superconductivity was observed in a wide pressure range from 1.5 to 7.6 GPa.We also investigated the transport properties in the external magnetic field in order to study a characteristic temperature dependence of the resistivity in the normal state. (C) 2002 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4526(01)01091-2

Spin dynamics of heavy fermion system LiV2O4 under high pressure Reviewed

K Fujiwara, H Yoshioka, K Miyoshi, J Takeuchi, TC Kobayashi, K Amaya

PHYSICA B-CONDENSED MATTER 312 913 - 915 2002.3

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

The nuclear spin lattice relaxation time (T-1) Li-7 in the heavy fermion system LiV2O4 has been measured under high pressure up to 3.7 GPa. At ambient pressure, 1/T-1 shows broad maximum around 50K and is proportional to the temperature below 8 K. This is apparently quite similar to the relaxation behavior in f-electron systems. However, 1/T-1 becomes larger with applying higher pressure below 10 K and does not obey T1T =constant relation down to I K. This pressure dependence of T, is opposite to that of Cc compounds, such as CeCu5.9Au0.1 and CeCu2Si2. Spin dynamics of LiV2O4 under pressure is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01492-2

A change of the Fermi surface across the metamagnetic transition under pressure in UGe2 Reviewed

Y Haga, M Nakashima, R Settai, S Ikeda, T Okubo, S Araki, TC Kobayashi, N Tateiwa, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 5 ) L125 - L135 2002.2

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

We have performed the de Haas-van Alphen (dHvA) and ac-susceptibility experiments on a ferromagnet UGe2 under pressure for the field along the easy a-axis. The p-H phase diagram was determined, indicating three kinds of phase: paramagnetic and weakly and strongly polarized phases. The detected dHvA frequencies as well as the cyclotron masses are found to be very different between the weakly and strongly polarized states. A change of the Fermi surface occurs when the weakly polarized phase is changed into the strongly polarized phase with increasing magnetic field.

DOI： 10.1088/0953-8984/14/5/103

Novel phases in the field-induced spin-density-wave state in (TMTSF)(2)PF6 Reviewed

AV Kornilov, VM Pudalov, Y Kitaoka, K Ishida, T Mito, JS Brooks, JS Qualls, JAAJ Perenboom, N Tateiwa, TC Kobayashi

PHYSICAL REVIEW B 65 ( 6 ) 2002.2

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

Magnetoresistance measurements on the quasi-one-dimensional organic conductor (TMTSF)(2)PF6 performed in magnetic fields B up to 16 T, temperatures T down to 0.12 K and under pressures P up to 14 kbar have revealed new phases on its P-B-T phase diagram. We found a new boundary which subdivides the field induced spin density wave (FISDW) phase diagram into two regions. Whereas a low-temperature region of the FISDW diagram is characterized by a hysteresis behavior typical for the first-order transitions, in a high-temperature region of the FISDW phase diagram, the hysteresis was found to disappear. We also found that the temperature dependence of the resistance (at a constant B) changes sign at about the same boundary, We compare these results with recent theoretical models.

DOI： 10.1103/PhysRevB.65.060404

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