Faculty Profiles - KOBAYASHI Tatsuo

Papers - KOBAYASHI Tatsuo

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A change of the Fermi surface in UGe2 across the critical pressure Reviewed

R Settai, M Nakashima, S Araki, Y Haga, TC Kobayashi, N Tateiwa, H Yamagami, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 1 ) L29 - L36 2002.1

Language：English Publisher：IOP PUBLISHING LTD

We carried out the de Haas-van Alphen (dHvA) experiment under pressure for a ferromagnet UGe2. The dHvA frequency of a main dHvA branch named a, that corresponds to a majority up-spin band 40-hole Fermi surface, decreases monotonously with increasing pressure, but in the pressure range from p(c)* (similar or equal to1.2 GPa) to p(c) (similar or equal to1.5 GPa) the dHvA signal disappears completely, where p(c) and p(c)* correspond to critical pressures for a Curie temperature T-C and the C second phase transition temperature T* (<T-C), respectively. For p > p(c) we observed new dHvA branches with large cyclotron masses of 19-64m(0), which correspond to main Fermi surfaces in the paramagnetic state.

DOI： 10.1088/0953-8984/14/1/104

Fermi surface, magnetic and superconducting properties of LaRhIn5 and CeTIn5 (T : Co, Rh and Ir) Reviewed

H Shishido, R Settai, D Aoki, S Ikeda, H Nakawaki, N Nakamura, T Iizuka, Y Inada, K Sugiyama, T Takeuchi, K Kindo, TC Kobayashi, Y Haga, H Harima, Y Aoki, T Namiki, H Sato, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 1 ) 162 - 173 2002.1

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

We have studied Fermi surface properties of LaRhIn5 and CeTIa(5) (T: Co, Rh and Ir) via the de Haasvan Alphen (dHvA) experiment. The Fermi surface of a non-4f reference compound LaRhIn5 is quasi-two dimensional, reflecting the unique tetragonal crystal structure, which is consistent with the result of FLAWP energy band calculations. The Fermi surface of an antiferromagnet CeRhIn5 is similar to that of LaRhIn5 although the cyclotron mass in CeRhIn5 is roughly by one order larger than that in LaRhIn5. Both Fermi surfaces are. however, different from those of CeCoIn5 and CcIrIn(5) which are well explained by the 4f-itinerant band model. The 4f electrons in CeRhIn5 thus do not contribute to the volume of ate Fermi surface. We have also studied magnetic and superconducting properties of CeCoIn5 and CeIrIn5.

DOI： 10.1143/JPSJ.71.162

Pressure-temperature phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3: In-115-NQR study under pressure Reviewed

S Kawasaki, T Mito, GQ Zheng, C Thessieu, Y Kawasaki, K Ishida, Y Kitaoka, T Muramatsu, TC Kobayashi, D Aoki, S Araki, Y Haga, R Settai, Y Onuki

PHYSICAL REVIEW B 65 ( 2 ) 020504-1 - 4 2002.1

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

We report the pressure (P)-temperature (T) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the In-115 nuclear-spin-lattice-relaxation (T-1) measurement. In the itinerant 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. In CeIn3, the localized magnetic character is robust against the application of pressure up to Psimilar to1.9 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.

DOI： 10.1103/PhysRevB.65.020504

Thermal Property of Heavy Fermion Compound YbP Reviewed

N. Tateiwa, T. Kobayashi, K. Amaya, D. X. Li, Y. Shiokawa, T. Suzuki

J. Phys. Soc. Jpn. 71 ( 5 ) 1365 - 1369 2002

Language：English Publishing type：Research paper (scientific journal) Publisher：The Physical Society of Japan (JPS)

Low-temperature specific heat and its field-dependence up to 16 T was measured in a stoichiometric single crystal of YbP. A sharp peak was observed at $T_{\text{N } } = 0.53$ K in zero magnetic field. Application of external field seems to induce a new magnetic phase above 11 T. The field dependence of the transition temperature in the high-field phase is different from that of the low field phase. The linear coefficient of the electronic specific heat is estimated as 120 mJ/mol$\cdot$K2 from low temperature specfic heat, suggesting heavy Fermion state in YbP.

DOI： 10.1143/JPSJ.71.1365

Other Link： https://jlc.jst.go.jp/DN/JALC/00156475165?from=CiNii

Evolution of pressure-induced heavy fermion state and superconductivity in (formula presented) 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. Ōnuki

Physical Review B - Condensed Matter and Materials Physics 66 ( 21 ) 1 - 5 2002

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

Evolution of the pressure-induced heavy fermion state and superconductivity in (formula presented) have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch (formula presented) increases from 5.5 (formula presented) at ambient pressure to 20 (formula presented) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 (formula presented) 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. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.214510

Thermal properties of a low carrier concentration compound YbP Reviewed

N. Tateiwa, T. C. Kobayashi, K. Amaya, D. Li, Y. Shiokawa, T. Suzuki

J. Phys. Soc. Jpn. 2002

Thermal properties of a ferromagnetic superconductor UGe2 Reviewed

Naoyuki Tateiwa, Tatsuo C. Kobayashi, Kichi Amaya, Yoshinori Haga, Rikio Settai, Yoshichika Onuki

Journal of Nuclear Science and Technology 39 195 - 198 2002

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

Thermal properties of a ferromagnetic superconductor UGe2 were investigated by the heat capacity measurements. The bulk nature of the superconductivity was confimied by the observation of a peak in the heat capacity at the superconducting transition temperature T SC, From the pressure dependence of the linear heat capacity coefficient γ, it is suggested that the low energy magnetic excitation near the critical point Pc*, where T* becomes OK, might play an important role on the superconductivity. The pressure dependence of the superconducting peak and the temperature dependence of CIT above T SC suggest that the order parameter of the superconducting state might be different between the phases below and above PC *. © 2002 Atomic Energy Society of Japan. All rights reserved.

DOI： 10.1080/00223131.2002.10875442

Magnetic - nonmagnetic transition of U3P4 at high pressures Reviewed

Keiki Takeda, Masashi Tanaka, Tatsuo C. Kobayashi, Teruhiko Akazawa, Katsuya Shimizu, Kiichi Amaya, Yoshihiko Inada, Piotr Wiśniewski, Dai Aoki, Etsuji Yamamoto, Yoshinori Haga, Yoshichika Ōnuki

Journal of Nuclear Science and Technology 39 191 - 194 2002

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

The transport properties of the itinerant ferromagnet U3P4 have been studied at high pressures up to 6.0 GPa using a diamond anvil cell. The Curie temperature TC decreases with increasing pressure, but then TC cannot be assigned above 4.0 GPa. The coefficient A, assuming the Fermi liquid behavior (p(T) = p0 + AT2) at low temperatures, shows a maximum at 5.3 GPa. The temperature dependence of the resistivity at 5.0 GPa follows T 5/3 which is expected in the SCR theory of a three dimensional ferromagnet. From these results, it is concluded that the ferromagnetic-nonmagnetic transition exists at around 5.0 GPa. © 2002 Atomic Energy Society of Japan. All rights reserved.

DOI： 10.1080/00223131.2002.10875441

Slow magnetization reversal in [Ni-4(OMe)(4)(sal(4)(MeOH)(4)] Reviewed

M Nakano, GE Matsubayashi, T Muramatsu, TC Kobayashi, K Amaya, J Yoo, G Christou, DN Hendrickson

MOLECULAR CRYSTALS AND LIQUID CRYSTALS 376 405 - 410 2002

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

The magnetic behavior of the nickel cubane complex [Ni-4(OMe)(4)(sal)(4)(MeOH)(4)] (Hsal = salicylaldehyde) was studied by using a Hartshorn bridge equipped with a He-3/He-4 dilution refrigerator. This complex has long been known to have a well-isolated high-spin ground state with S = 4 and it was suggested to have an easy-axis type anisotropy. AC magnetic susceptibility data clearly show a slow magnetization reversal below 0.3 K, characteristic of single-molecule magnets. The Arrhenius plot of the relaxation rate provides the activation energy of about 5 K.

Pressure-temperature phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3: 115In−NQR study under pressure Reviewed

S. Kawasaki, T. Mito, G.-q. Zheng, C. Thessieu, Y. Kawasaki, K. Ishida, Y. Kitaoka, T. Muramatsu, T. C. Kobayashi, D. Aoki, S. Araki, Y. Haga, R. Settai, Y. Ōnuki

Physical Review B 65 ( 2 ) 2001.12

Fermi surface instability in CeRh2Si2 under pressure Reviewed

S. Araki, R. Settai, T. C. Kobayashi, H. Harima, Y. Onuki

Physical Review B - Condensed Matter and Materials Physics 64 ( 22 ) 2244171 - 2244177 2001.12

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

That the 4f electrons in the rare-earth antiferromagnetic compound CeRh2Si2 should be considered as localized electrons at cerium sites has been confirmed by comparing a de Haas-van Alphen experiment to the result of energy band calculations for LaRh2Si2. When pressure p is applied to the compound, the Néel temperature TNI=36 K decreases and finally becomes zero at pc≃1.0-1.1 GPa. The topology of the Fermi surface is found to be almost unchanged up to 1.0 GPa, but the cyclotron effective mass increases with increasing pressure. Above 1.1 GPa, the topology of the Fermi surface changes abruptly. A new Fermi surface is explained by the 4f-itinerant-band model. The corresponding cyclotron mass is large, being about 22m0.

Fermi surface instability in CeRh2Si2 under pressure Reviewed

S Araki, R Settai, TC Kobayashi, H Harima, Y Onuki

PHYSICAL REVIEW B 64 ( 22 ) 2001.12

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

That the 4f electrons in the rare-earth antiferromagnetic compound CeRh2Si2 should be considered as localized electrons at cerium sites has been confirmed by comparing a de Haas-van Alphen experiment to the result of energy band calculations for LaRh2Si2. When pressure p is applied to the compound, the Neel temperature T-N1 = 36 K decreases and finally becomes zero at p(c)similar or equal to1.0-1.1 GPa. The topology of the Fermi surface is found to be almost unchanged up to 1.0 GPa, but the cyclotron effective mass increases with increasing pressure. Above 1.1 GPa, the topology of the Fermi surface changes abruptly. A new Fermi surface is explained by the 4f-itinerant-band model. The corresponding cyclotron mass is large, being about 22m(o).

DOI： 10.1103/PhysRevB.64.224417

Superconductivity of CeRhIn5 under high pressure Reviewed

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 11 ) 3362 - 3367 2001.11

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

The pressure dependence of transport properties in CeRhIn5 was studied up to 8.5 GPa by using a diamond-anvil cell. The electrical resistivity does not follow the T-2-dependecne of a Fermi liquid nature under any pressure. In this non-Fermi liquid state, superconductivity was observed in a wide pressure range of 1.5 GPa < P < 7.6 GPa. The superconducting temperature TC has a double-maximum structure with a minimum at 5.2 GPa. A maximum of T-C = 2.2 K was observed at P = 2.5 GPa, where the corresponding electrical resistivity just above TC has the maximum. The upper critical field H-C2 and the magnetoresistances were also investigated under pressure.

DOI： 10.1143/JPSJ.70.3362

Magnetic properties of a pressure-induced superconductor UGe2 Reviewed

N Tateiwa, K Hanazono, TC Kobayashi, K Amaya, T Inoue, K Kindo, Y Koike, N Metoki, Y Haga, R Settai, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 10 ) 2876 - 2879 2001.10

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

We performed DC-magnetization and neutron scattering experiments under pressure P for a pressure-induced superconductor UGe2. We found that the magnetic moment is enhanced at a characteristic temperature T* in the ferromagnetic state, where T* is smaller than a Curie temperature T-C. This enhancement becomes remarkable in the vicinity of P-C* = 1.20 GPa, where T* becomes 0 K and the superconducting transition temperature T-SC shows a maximum. The characteristic temperature T*, which decreases with increasing pressure, also depends on the magnetic field.

DOI： 10.1143/JPSJ.70.2876

Pressure-induced superconductivity in a ferromagnet UGe2 (vol 13, pg L17, 2001) Reviewed

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

JOURNAL OF PHYSICS-CONDENSED MATTER 13 ( 29 ) 6443 - 6443 2001.7

Neutron scattering study of linear-chain Haldane compounds NDMAZ and NDMAP Reviewed

N Metoki, Y Koike, Y Matsuoka, T Kobayashi, M Yamashita

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 226 414 - 416 2001.5

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

Neutron scattering experiments were carried out for the new Haldane compounds Ni(C5H14N2)(2)N-3(ClO4) (NDMAZ) and Ni(C5H14N2)(2)N-3(PF6) (NDMAP) in the magnetic field up to 10 T in order to investigate the field-induced long-range ordering and the spin excitation. For NDMAZ. the triplet excited state (1.61, 1.76, and 3.2 meV) and field dependence of these levels were observed at Q = (000.5). From these data. the intra-chain coupling constant approximate to 4.3 meV and the anisotropic parameters D approximate to 0.76 meV and /E/ approximate to 0.038 meV were estimated. For NDMAP the gap was observed at about 0.48 and 0.64 meV at Q (000.5). By applying the field of 5 T, the first excited state shifted below the resolution less than 0.13 meV. Above the critical field H-C, the intensities of singlet-triplet excitation becomes very weak. This work is the first neutron scattering study on a Haldane system above the critical fields. (C) 2001 Elsevier Science B.V. All rights reserved.

Proton NMR study of the field-induced long-range ordering in Haldane gap system NDMAP Reviewed

TC Kobayashi, K Tanaka, K Fujiwara, K Amaya, N Aizawa, T Ishii, M Yamashita

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 226 423 - 424 2001.5

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

Appearance of the field-induced long-range ordering was observed directly by a proton NMR measurement in Haldane gap system, Ni(C5H14N2)(2)N-3(PF6) (NDMAP). A sudden splitting of the spectrum due to the appearance of the transverse staggered moment was observed just below T-N. The transverse staggered moment is estimated as 1.1 mu (B) in the external field of 10.9 T parallel to the ab-plane. (C) 2001 Elsevier Science B.V. All rights reserved.

Field-induced long-range ordering in Haldane gap system NDMAZ Reviewed

TC Kobayashi, H Tatewaki, A Koda, K Amaya, Y Narumi, K Kindo, N Aizawa, T Ishii, M Yamashita

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 3 ) 813 - 817 2001.3

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

Field-induced long-range ordering is investigated by heat capacity and high-field magnetization measurements in Haldane gap system Ni(C5H14N2)(2)N-3(ClO4) (NDMAZ). In the high-field magnetization measurement along the crystal c-axis, the differential magnetization is found to reveal the characteristic peak corresponding to the phase transition to the ordered state. The magnetization increases as (H - H-C)(0.6) at the lowest temperature. The phase boundary determined down to 44 mK by the peak of the differential magnetization obeys T-N similar to (H - H-C)(0.45). Anisotropic phase diagram is similar to that of Ni(C5H14N2)(2)N-3(PF6) (NDMAP).

DOI： 10.1143/JPSJ.70.813

High-field magnetization of URu2Si2 under high pressure Reviewed

T Inoue, K Kindo, H Okuni, K Sugiyama, Y Haga, E Yamamoto, TC Kobayashi, Y Uwatoko, Y Onuki

PHYSICA B 294 271 - 275 2001.1

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

The temperature dependence of the magnetic susceptibility and the high-field magnetization up to 55T are measured for URu2Si2 under high pressures up to 1 GPa. Both T-chi max and T-N in the susceptibility increase with increasing pressure. The Value of the susceptibility below T-chi max decreases with increasing pressure. The three high-held metamagnetic transitions at H-c1 = 35.1T, H-c2 = 36.5 T and H-c3 = 39.6 T at ambient pressure, show different pressure-dependent behaviors. The metamagnetic transition at H-c1 broadens but survives and its transition field increases with increasing pressure. However, the transition at H-c2 is smeared out and disappears above 0.4 GPa. The transition at H-c3 broadens more clearly than the transition at H-c1. The fact that both T-chi max and the metamagnetic transition fields increase suggests that the interaction between the f-electrons and the conduction electrons is enhanced by pressure. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(00)00657-8

Pressure-induced superconductivity in a ferromagnet UGe2 Reviewed

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

JOURNAL OF PHYSICS-CONDENSED MATTER 13 ( 1 ) L17 - L23 2001.1

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

We confirmed bulk-superconductivity of a ferromagnet UGe2 by the specific heat measurement, together with the measurements of the electrical resistivity and ac susceptibility, in a pressure range from p = 1.0 to 1.5 GPa, where the Curie temperature T-C(= 22-36 K) is still high, but another characteristic temperature T* is close to zero. In this pressure range, the heavy fermion state is found to be formed at low temperatures.

DOI： 10.1088/0953-8984/13/1/103

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