Faculty Profiles - KOBAYASHI Tatsuo

Papers - KOBAYASHI Tatsuo

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Hall Effect in Single Crystal CeCu2Si2 under High Pressure Reviewed

S. Araki, Y. Shiroyama, T. Shinohara, Y. Ikeda, T. C. Kobayashi, S. Seiro, C. Geibel, F. Steglich

Journal of Physics: Conference Series 391 012005 2012

Cu-NQR of CeCu2Si2 under High Pressure Reviewed

K. Fujiwara, Y. Okazaki, K. Miyoshi, J. Takeuchi, Y. Ikeda, T. C. Kobayashi, C. Geibel, F. Steglich

Journal of Physics: Conference Series 391 012012 2012

Interplay of Superconductivity and Fermi-Liquid Transport in Rh-Doped CaFe2As2 with Lattice-Collapse Transition Reviewed

Masataka Danura, Kazutaka Kudo, Yoshihiro Oshiro, Shingo Araki, Tatsuo C. Kobayashi, Minoru Nohara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( 10 ) 103701-1-103701-4 2011.10

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

Ca(Fe1-xRhx)(2)As-2 undergoes successive phase transitions with increasing Rh doping in the T = 0 limit. The antiferromagnetic-metal phase with orthorhombic structure at 0.00 <= x <= 0.020 is driven to a superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020 <= x <= 0.024; a non-superconducting collapsed-tetragonal (cT) phase takes over at x >= 0.024. The breakdown of Fermi-liquid transport is observed in the ucT phase above T-c. In the adjacent cT phase, Fermi-liquid transport is restored along with a disappearance of superconductivity. This interplay of superconductivity and Fermi-liquid transport suggests the essential role of magnetic fluctuations in the emergence of superconductivity in doped CaFe2As2.

DOI： 10.1143/JPSJ.80.103701

Pressure-induced structural phase transitions in UIr Reviewed

H. Kotegawa, S. Araki, T. Akazawa, A. Hori, Y. Irie, S. Fukushima, H. Hidaka, T. C. Kobayashi, K. Takeda, Y. Ohishi, K. Murata, E. Yamamoto, S. Ikeda, Y. Haga, R. Settai, Y. Onuki

PHYSICAL REVIEW B 84 ( 5 ) 054524-1-054524-5 2011.8

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

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

Hall effect in CeCu2Si2 under pressure Reviewed

Shingo Araki, Yuki Shiroyama, Yoichi Ikeda, Tatsuo C. Kobayashi, Silvia Seiro, Christoph Geibel, Frank Steglich

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( Suppl. A ) SA034-1-SA034-3 2011.7

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

We report the results of Hall effect measurements on CeCu2Si2 under high pressures up to 4.8 GPa. The Hall coefficient at ambient pressure increases with decreasing temperature and exhibits maximum at 4 K. The Hall coefficient at temperature higher than the coherent temperature of 10 K is consistent with the anomalous Hall effect. The pressure effect on the temperature dependence of the Hall coefficient is not simple. The pressure dependence of the Hall coefficient shows anomaly from 3.1 to 4.8 GPa, where the superconductivity is enhanced. These results indicate the close relationship between the Hall coefficient and the superconductivity.

DOI： 10.1143/JPSJS.80SA.SA061

Superconductivity of Heavy Carriers in the Pressure-Induced Phases of Cd2Re2O7 Reviewed

Tatsuo C. Kobayashi, Yuta Irie, Jun-ichi Yamaura, Zenji Hiroi, Keizo Murata

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( 2 ) 023715 2011.2

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

The superconductivity of Cd2Re2O7 is investigated under hydrostatic pressures up to 4.6 GPa by means of electrical resistivity. A rich phase diagram is obtained, which contains at least five new pressure-induced phases in addition to the three already present at ambient pressure, revealing inherent structural and electronic instabilities of the compound. We find large enhancements of more than one order of magnitude in the upper critical field as well as in the coefficient of the T-2 term in resistivity at around a critical pressure of 4.2 GPa, where an inversion-symmetry-breaking structural transition tends to disappear. Heavy fermion superconductivity is probably realized under high pressures in Cd2Re2O7, which is extraordinary for d-electron compounds.

DOI： 10.1143/JPSJ.80.023715

Incommensurate guest adsorption in bellows-shaped one-dimensional channels of porous coordination polymers Reviewed

Ryotaro Matsuda, Ryo Kitaura, Yoshiki Kubota, Tatsuo C. Kobayashi, Masaki Takata, Susumu Kitagawa

MICROPOROUS AND MESOPOROUS MATERIALS 129 ( 3 ) 296 - 303 2010.4

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

Adsorption isotherms of N-2, O-2, CO2, and Xe on a flexible microporous coordination polymer, CPL-2 [Cu-2(pzdc)(2)(bpy)]center dot(pzdc = pyrazine-2,3-dicarboxylate; bpy = 4,4'-bipyridine), possessing bellows-shaped one-dimensional channels were measured. A nonintegral number of each of the N-2, O-2, CO2, and Xe molecules can be accommodated in each unit pore, which indicates that all guest molecules are accommoda dated in the so-called "incommensurate fashion". in situ synchrotron X-ray powder diffraction patterns of CPL-2 with guest molecules were recorded. The unit cells were determined from each pattern. It Was found that the host CPL-2 exhibits different crystal transformation with the accommodation of each guest molecule. This indicates that, even in the case of incommensurate adsorption, the flexible framework of a microporous coordination polymer can transform each pore to suit different guest molecules. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.micromeso.2009.06.023

Magnetic Properties and the Arrangement of Molecular Oxygen Adsorbed in the Microporous Coordination Polymer Cd(bpndc)(bpy) Reviewed

A. Hori, T. Yamaguchi, T. C. Kobayashi, A. Matsuo, K. Kindo, D. Tanaka, S. Kitagawa

Journal of Low Temperature Physics 159 ( 1-2 ) 122 - 125 2010.4

NQR study of pressure induced superconductivity in CeCu2Si2 Reviewed

K. Fujiware, Y. Okazaki, Y. Hata, K. Miyoshi, J. Takeuchi, T. C. Kobayashi, C. Geibel, F. Steglich

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 247 ( 3 ) 608 - 610 2010.3

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

We have measured nuclear quadrupole resonance (NQR) for Cu-63 nuclei under high pressure up to 4.8 GPa. A linear increase in NQR frequency (63)nu(Q) of Cu-63 nuclei was observed below 3 GPa. However, (63)nu(Q) deviates gradually from the linear relation above 3.5 GPa. The downward deviation is associated with a change of valence and consistent with the results of band calculations with the structural parameters under pressure. Antiferromagnetic (AFM) spin fluctuations are drastically suppressed with increasing pressure, whereas T-c increases from 0.7 K at ambient pressure to 1.64K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level.
[GRAPHICS]
These are indenter pressure cells for NQR measurements. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200983050

High-field magnetization process of O<inf>2</inf> adsorbed in a microporous coordination polymer CPL-1 at various temperatures Reviewed

A. Hori, T. C. Kobayashi, A. Matsuo, K. Kindo, R. Matsuda, S. Kitagawa

Journal of Physics: Conference Series 200 2010.1

High-field magnetization measurements have been performed at various temperatures on the molecular oxygen adsorbed in a microporous coordination polymer CPL-1. Molecular oxygen with S = 1 forms O2-O2 dimer in the nanochannels of CPL-1. The magnetic properties can be explained by not the S = 1 Heisenberg antiferromagnetic dimer model but the O 2-O2 dimer model taking into account the spin-dependent intermolecular potential. This feature is attributed to the fact that the magnetic interaction between O2 is comparable to the van der Waals force. ? 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/200/2/022018

Pressure and magnetic field tuned quantum critical point in the Kondo antiferromagnet CePtZn Reviewed

S. K. Dhar, R. Kulkarni, H. Hidaka, Y. Toda, H. Kotegawa, T. C. Kobayashi, P. Manfrinetti, A. Provino

JOURNAL OF PHYSICS-CONDENSED MATTER 21 ( 15 ) 156001 2009.4

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

We report magnetization, heat capacity and electrical resistivity measurements on CePtZn, which crystallizes in the orthorhombic TiNiSi type structure. Magnetization and electrical resistivity on the iso-structural series of compounds Ce1-xLaxPtZn (x = 0.1, 0.2 0.5 and 1) were also carried out. The electrical resistivity of CePtZn was also measured in external magnetic fields up to 12 T and under pressures up to 2.66 GPa. We find that CePtZn is a dense Kondo lattice, ordering antiferromagnetically at T-N = 1.7 K, with a comparable Kondo temperature. The magnetic transition temperature, T-N, is continuously suppressed both by the magnetic field and pressure and T-N. 0 around 5-6 T and at 1.2 GPa, respectively. Non-Fermi liquid behavior of resistivity at 4 T and 1.2 GPa and logarithmic divergence of the heat capacity, C-4f/T, at 6 T in a limited temperature region strongly suggest the emergence of a quantum critical point as T-N -> 0.

DOI： 10.1088/0953-8984/21/15/156001

Pressure Effect on Yb-Based Strongly Correlated Electron Systems Reviewed

T. Mito, M. Otani, M. Nakamura, T. Koyama, S. Wada, H. Kotegawa, T. C. Kobayashi, B. Idzikowski, M. Reiffers, J. L. Sarrao

ACTA PHYSICA POLONICA A 115 ( 1 ) 47 - 52 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：POLISH ACAD SCIENCES INST PHYSICS

We studied pressure effects on YbCu(5) and YbInCu(4), good examples of the Yb-based compounds to investigate the nonmagnetic-magnetic transition in Yb-based strongly correlated electron systems. With increasing pressure, the low-temperature Fermi liquid state of YbCu(5) is gradually suppressed, suggesting the second-order like nonmagnetic-magnetic transition around the pressure of 5-6 GPa. On the other hand, in YbInCu(4) which has a pressure-induced magnetic ordered ground state above P(C) = 2.45 GPa, both high-temperature paramagnetic and low-temperature intermediate valence phases are insensitive to pressure. Our results confirm the first-order nature of the transition between the intermediate valence and magnetic ordered phases with pressure.

Hindered Rotation of Methane Molecules in the One-Dimensional Nanochannel of a Porous Coordination Polymer Reviewed

Yoshiki Kubota, Masaki Takata, Ryo Kitaura, Ryotaro Matsuda, Tatsuo C. Kobayashi, Susumu Kitagawa

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 ( 1 ) 69 - 76 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER SCIENTIFIC PUBLISHERS

The crystal structure of a microporous coordination polymer with adsorbed methane gas was determined by in situ synchrotron powder diffraction of the gas adsorption and the MEM (maximum entropy method)/Rietveld method. Methane molecules were found to be adsorbed forming a one-dimensional array in the nanochannels of the polymer. The MEM charge density distribution of the adsorbed methane molecules indicated some protrusions which were not observed in that of a spherical atom of adsorbed argon. This was interpreted as a mixed distribution of two uniaxially rotating molecules with different pivotal axes. The methane molecules displayed hindered rotation depending on the shape of the nanopore surface. This result indicates the capability to control the molecular arrangement and orientation by the adsorption of gas molecules on the precisely designed nanopores of coordination polymers.

DOI： 10.1166/jnn.2009.J085

High Pressure NQR Measurement in CeCu2Si2 up to Sudden Disappearance of Superconductivity Reviewed

Kenji Fujiwara, Yoshiki Hata, Keigo Kobayashi, Kiyotaka Miyoshi, Jun Takeuchi, Yoshiyuki Shimaoka, Hisashi Kotegawai, Tatsuo C. Kobayashi, Christoph Geibel, Frank Steglich

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( 12 ) 123711 2008.12

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

We report the results of Cu-63 nuclear quadrupole resonance (NQR) measurements on CeCu2Si2 under high pressures up to 4.8GPa. Enhanced spin fluctuations due to quantum criticality at ambient pressure are drastically suppressed with increasing pressure, whereas T-c increases from 0.7 K at ambient pressure to 1.64K at 4.2GPa. We have found that bulk superconductivity suddenly disappears at 4.8GPa accompanied with a rapid decrease in the density of states at the Fermi level. The nuclear spin-lattice relaxation rate 1/T-1 at 4.2 GPa reveals that anisotropic superconductivity in the strong-coupling regime is realized even under high pressure far from the antiferromagnetic critical point. Superconductivity under high pressure is unconventional in origin, but the spin fluctuation scenario is not likely to be applicable.

DOI： 10.1143/JPSJ.77.123711

Unconventional superconductivity in f-electron systems Reviewed

Y. Onuki, R. Settai, T. Takeuchi, Y. Haga, E. Yamamoto, N. Tateiwa, M. Nakashima, H. Shishido, T. C. Kobayashi, D. Aoki

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 53 ( 2 ) 1034 - 1040 2008.8

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

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.

Dependence of pressure-induced phase transitions on pressure-transmitting media in the heavy-electron superconductor URu2Si2 Reviewed

H. Amitsuka, K. Matsuda, M. Yokoyama, I. Kawasaki, S. Takayama, Y. Ishihara, K. Tenya, N. Tatelwa, T. C. Kobayashi, H. Yoshizawa

PHYSICA B-CONDENSED MATTER 403 ( 5-9 ) 925 - 927 2008.4

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

Elastic neutron-scattering and ac-susceptibility measurements have been performed on a 20 single crystal of URu2Si2 under hydrostatic pressure up to similar to 1.1 GPa using Fluorinert 70 & 77 and Daphne oil 7373 as pressure-transmitting media. Daphne oil produces better hydrostaticity of the applied pressure than Fluorinert, resulting in a slight shift of the phase boundary between hidden order and antiferromagnetic order to a lower pressure. The superconducting phase is also influenced, but never overlaps with the antiferromagnetic phase. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.065

Observation of charge fluctuations in skutterudite compounds through an Sb-NQR measurement Reviewed

H. Kotegawa, Y. Irie, H. Hidaka, T. C. Kobayashi, D. Kikuchi, H. Sugawara, H. Sato

PHYSICA B-CONDENSED MATTER 403 ( 5-9 ) 772 - 774 2008.4

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

We report that the nuclear spin-spin relaxation rate 1/T-2 shows characteristic peaks in the skutterudite compounds of ROs4Sb12 (R = La, Pr, Nd, and Sm) and PrRu4Sb12. The broadening of Sb-NQR spectrum accompanied with the peak in 1/T-2 suggests that some charge fluctuation exists in these systems and slows down around the peak in 1/T-2. The peaks in 1/T-2 appear around 120 K in all the systems we measured, while the other peaks around 20 K are observed in ROs4Sb12 (R = Pr, Nd, and Sm). The 12 Sb sites are not equivalent at low temperatures in these compounds. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.226

Evolution of transport and low-energy spin fluctuations in YbXCu4(X = Au and Pd) with the application of magnetic field Reviewed

A. Yamamoto, T. Yokoyama, S. Wada, K. Tabira, H. Kotegawa, T. C. Kobayashi, J. L. Sarrao

PHYSICA B-CONDENSED MATTER 403 ( 5-9 ) 1205 - 1207 2008.4

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

We have investigated evolution of transport and low-energy spin fluctuation properties of heavy Fermi liquid compounds YbAuCu4 and YbPdCu4 with the application of magnetic field. YbAuCu4 is found to be driven from the originally antiferromagnetically (AFM) ordered ground state (T-N similar to 0.8K) to a nonmagnetic Fermi liquid (FL) one through the field-tuned quantum critical point (QCP) at H-cr similar or equal to 13 kOe (T-N -> 0). In the vicinity of H-cr, the electrical resistivity measurement provides evidence for the increase in the inelastic scattering of heavy electrons, and the Cu-63 Spin-lattice relaxation rate measurement exhibits the occurrence of AFM spin order instability. Whilst, YbPdCu4 transforms from the originally ferromagnetically (FM) ordered ground state (T-C similar to 0.6K) into the nonmagnetic FL state, without any intermediate NFL phenomena. This result indicates that the competition of the field-stabilized FM correlation and field-destabilized AFM correlation plays an important role on the field-driven quantum critical phenomena. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.325

de Haas-van Alphen study of the Pr-based filled skutterudite PrOs4P12 Reviewed

Hitoshi Sugawara, Yoshinori Iwahashi, Ko-ichi Magishi, Takahito Saito, Kuniyuki Koyama, Hisatomo Harima, Daisuke Kikuchi, Hideyuki Sato, Toyoaki Endo, Rikio Settai, Yoshichika Onuki, Naoki Wada, Hisashi Kotegawa, Tatsuo C. Kobayashi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( Suppl. A ) 108 - 113 2008.1

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

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

Anomalous Kondo Effect and Ordered State in Heavy Fermion System SmOs4Sb12 : Resistivity, Sb-NQR, and Magnetization Measurements under High Pressure Reviewed

Hisashi Kotegawa, Keisuke Tabira, Yuta Irie, Hiroyuki Hidaka, Tatuo C. Kobayashi, Daisuke Kikuchi, Kenya Tanaka, Sho Tatsuoka, Hitoshi Sugawara, Hideyuki Sato

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( Suppl. A ) 90 - 95 2008.1

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

We report resistivity, nuclear quadrupole resonance (NQR), and magnetization measurements under high pressures in a novel heavy fermion compounds SmOs4Sb12. The resistivity and nuclear spin-lattice relaxation rate 1/T-1 show the coherent behavior below a characteristic temperature T* = 20 - 25 K at ambient pressure. Nuclear spin-spin relaxation rate 1/T-2 was found to show a peak of electrical origin around T*. Some charge fluctuation is considered to play an important role in the Kondo effect of SmOs4Sb12. On the other hand, the magnetization at low temperature does not increase under pressures, although the transition temperature increases. The NQR signals are strongly suppressed around the transition temperature and vanishes at low temperatures. These suggest that the ordered state in SmOs4Sb12 is not simple ferromagnetism.

DOI： 10.1143/JPSJS.77SA.90

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