Faculty Profiles - KOBAYASHI Tatsuo

Papers - KOBAYASHI Tatsuo

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Sb-NQR study of PrOs4Sb12 under high pressure Reviewed

Shinji Kawasaki, Kouta Katayama, Masahide Nishiyama, Hisashi Kotegawa, Tatsuo C. Kobayashi, Hitoshi Sugawara, Daisuke Kikuchi, Hideyuki Sato, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( Suppl. A ) 330 - 332 2008.1

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

We report Sb-123 nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs4Sb12 under high pressure. The temperature dependence of NQR frequency and spin-lattice relaxation rate 1/T-1 indicate that the crystal electric field splitting Delta(CEF) between the ground state Gamma(1) singlet and the first excited state Gamma((2))(4) 4 triplet decreases with increasing pressure. However, it is found Delta(CEF) and T-c stay constant above P similar to 2 GPa revealed by Sb-NQR up to P = 3.82 GPa for the first time. Remarkably, the temperature dependence of 1/T1 below T-c = 1.55 K at P = 1.91 GPa shows no coherence peak just below Tc and power-law behavior well below Tc in contrast to the exponential decrease observed at P = 0. Present results indicate the superconductivity in PrOs4Sb12 under pressure has nodes in the superconducting gap function.

DOI： 10.1143/JPSJS.77SA.330

Pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3: An 115In-NQR study under pressure Reviewed

S. Kawasaki, M. Yashima, Y. Kitaoka, K. Takeda, K. Shimizu, Y. Oishi, M. Takata, T. C. Kobayashi, H. Harima, S. Araki, H. Shishido, R. Settai, Y. Onuki

Phys. Rev. B 77 ( 6 ) 064508-1-064508-12 2008

Appearance of Pressure-Induced Magnetic Phase in $\alpha$-Manganese Reviewed

Takeda Keiki, Miyake Atsushi, Shimizu Katsuya, Kobayashi Tatsuo C., Amaya Kiichi

J Phys Soc Jpn 77 ( 2 ) 25001-1-25001-2 - 025001-2 2008

Kinetic gate-opening process in a flexible porous coordination polymer Reviewed

Daisuke Tanaka, Keiji Nakagawa, Masakazu Higuchi, Satoshi Horike, Yoshiki Kubota, Latsuo C. Kobayashi, Masaki Takata, Susumu Kitagawa

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 47 ( 21 ) 3914 - 3918 2008

Observation of gas molecules adsorbed in the nanochannels of porous coordination polymers by the in situ synchrotron powder diffraction experiment and the MEM/Rietveld charge density analysis Reviewed

Yoshiki Kubota, Masaki Takata, Tatsuo C. Kobayashi, S. Kitagawa

COORDINATION CHEMISTRY REVIEWS 251 ( 21-24 ) 2510 - 2521 2007.11

Language：English Publisher：ELSEVIER SCIENCE SA

Microporous coordination polymers have attracted attention for their numerous nanotechnology and engineering applications. Nano-coordination space provides some unique properties and functions that could never be realized in conventional porous materials. For the strategy of rational designs and the syntheses of novel porous coordination polymers, the structural information of adsorbed guest molecules inside the nanopores and the host framework is very important. In the present study, we describe the technique of the direct observation of gas molecules adsorbed in the nanochannels of porous coordination polymers by the in situ synchrotron powder diffraction measurement of gas adsorption and the maximum entropy method (MEM)/Rietveld charge density analysis. Specific alignment and properties of molecular oxygen obtained by gas adsorption in the nano-coordination space are revealed. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ccr.2007.07.025

Connection between charge fluctuations and the coherent temperature in the heavy-fermion system SmOs4Sb12 :: A Sb-121,Sb-123 NQR study Reviewed

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

PHYSICAL REVIEW LETTERS 99 ( 15 ) 156408-1-156408-4 2007.10

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

We report Sb-121,Sb- 123 nuclear quadrupole resonance measurements under pressure in a novel heavy fermion (HF) system SmOs4Sb12. The nuclear spin-spin relaxation rate 1/T-2 exhibits a distinct peak near the coherent temperature of the Kondo effect. The isotope effect of Sb-121 and Sb-123 indicates that the peak in 1/T-2 is electrical in origin. The connection between the peak in 1/T-2 and the development of coherency of the Kondo effect is robust even under pressure. It is conjectured that charge fluctuation plays an important role in forming the HF state in SmOs4Sb12.

DOI： 10.1103/PhysRevLett.99.156408

Pressure-temperature phase diagram and superconductivity in UIr Reviewed

Tatsuo C. Kobayashi, Akihiro Hori, Satoshi Fukushima, Hiroyuki Hidaka, Hisashi Kotegawa, Teruhiko Akazawa, Keiki Takeda, Yasuo Ohishi, Etsuji Yamamoto

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 5 ) 51007-1 -51007-11 2007.5

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

Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure-temperature phase diagram has been investigated by means of the electrical resistivity, ac-susceptibility and magnetization measurements under high pressure. The phase diagram consists of three magnetic phases FM1-3 and a superconducting phase. The huge enhancement of residual resistivity and the negative magnetoresistance are found in the intermediate pressure region. These behavior may be induced by the pressure-induced structural phase transition and the accompanied phase separation in this pressure range. The superconducting phase with narrow pressure range is embedded in the FM3 phase, adjacent to zero-temperature FM3-to-nonmagnetic transition. The temperature dependence of resistivity above T-SC follows non-Fermi liquid form of T-1.6. From these experimental facts, superconductivity is considered to be associated with the ferromagnetic fluctuation.

DOI： 10.1143/JPSJ.76.051007

Pressure-temperature phase diagrams of some heavy fermion systems Reviewed

T. C. Kobayashi, H. Hidaka, T. Fujiwara, M. Tanaka, K. Takeda, T. Akazawa, K. Shimizu, S. Kirita, R. Asai, H. Nakawaki, M. Nakashima, R. Settai, E. Yamamoto, Y. Haga, Y. Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 19 ( 12 ) 125205-1-125205-9 2007.3

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

We have studied the pressure-temperature phase diagrams in UIr, U3P4, UP2, CeAgSb2 and CeMg2Cu9 by means of the electrical resistivity. Application of pressure suppresses the magnetic ordering shown at ambient pressure in all compounds. In UIr, the pressure-induced superconductivity is observed in the vicinity of the magnetic-nonmagnetic transition. In this article, we review the pressure-temperature phase diagram and the properties of the magnetic nonmagnetic transition in these compounds.

DOI： 10.1088/0953-8984/19/12/125205

Drastic change of the electronic states at the quantum critical point in heavy fermions Reviewed

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 541 - 547 2007.3

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

We studied the change of the Fermi surface properties in antiferromagnets CeIn3 and CeRhIn5 via the dHvA experiments under pressure. We found the abrupt change of the Fermi surface at the critical pressure P-c, where the magnetic ordering state changes to the paramagnetic one. The change of the Fermi surface indicates that the 4f-electron character is changed from localized to itinerant in CeIn3 and CeRhIn5 at P-c. Namely, the 4f-electron contributes to the volume of the Fermi surface above P-c. Interestingly, the pressure-induced heavy fermion state with large effective mass was observed around P-c, where the pressure-induced superconductivity appears. We also discuss the Fermi surface properties in the system without inversion symmetry in the crystal structure as in CePt3Si and CeTX3 (T:Co, Ir, Rh, X: Si, Ge). The spin-orbit interaction due to the lack of inversion symmetry brings about a splitting of the Fermi surface, which is important for considering the formation of Cooper pair. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.11.197

Ge-73-NQR study of heavy-fermion compound CeNi2Ge2 Reviewed

S. Kawasaki, T. Sada, T. Miyoshi, H. Kotegawa, H. Mukuda, Y. Kitaoka, T. C. Kobayashi, T. Fukuhara, K. Maezawa, K. M. Itoh, E. E. Haller

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 590 - 592 2007.3

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

We report 73 Ge-nuclear-quadrupole resonance (NQR) study of heavy-fermion compound CeNi2Ge2. The temperature dependence of the 73 Ge nuclear-spin-lattice-relaxation rate 1/T-1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than T-FL 0.4K, where 1/T1T is constant. The 1/T1T decrease below T(NQR)c 0.1K, whereas resistance decreases below T (onset)c = 0.2K and does not become zero. These results indicate CeNi2Ge2 closely locates to a superconducting quantum critical point. (c) 2006 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.232

High-quality single crystal growth and physical properties in a ferromagnet UIr Reviewed

E. Yamamoto, Y. Haga, S. Ikeda, T. D. Matsuda, T. Akazawa, H. Kotegawa, T. C. Kobayashi, Y. Onuki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) E123 - E125 2007.3

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

UIr crystallizes in the monoclinic crystal structure without inversion symmetry. The magnetization measurement indicated that UIr is an Ising-type ferromagnet with the Curie temperature T-C1 = 46K at ambient pressure. We grew a high-quality single crystal by the Czochralski method in a tetra-arc furnace. The ingot was annealed under high vacuum by the solid state electrotransport method. Superconductivity with a transition temperature T-sc = 0.14 K was found under pressure. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.292

Effect of uniaxial stress on pressure-induced metal-insulator transition in PrFe4P12 Reviewed

Hiroyuki Hidaka, Naoki Wada, Hisashi Kotegawa, Tatsuo C. Kobayashi, Daisuke Kikuchi, Hideyuki Sato, Hitoshi Sugawara

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) E228 - E230 2007.3

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

We have carried out electrical resistivity measurements on PrFe4P12 under high pressure using some kinds of pressure-transmitting mediums in order to investigate the effect of uniaxial stress on a pressure-induced metal-insulator (M-I) transition. In the measurement under uniaxial stress, the M-I transition appears at a lower pressure than in the case of quasi-hydrostatic pressure, indicating that the uniaxial stress is favorable to the insulating phase. On the other hand, the M-I transition appears suddenly with finite M-I transition temperature between 2.55 and 2.66 GPa in the measurement under hydrostatic pressure. This fact suggests that the transition from the antiferroquadrupolar metallic phase to the insulating phase is of first order. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.1074

Nonmagnetic indenter-type high-pressure cell for magnetic measurements Reviewed

T. C. Kobayashi, H. Hidaka, H. Kotegawa, K. Fujiwara, M. I. Eremets

REVIEW OF SCIENTIFIC INSTRUMENTS 78 ( 2 ) 23909-1-23909-5 2007.2

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

An indenter-type high-pressure cell has been developed for electric and magnetic measurements in low-temperature and high-magnetic-field environments. The maximum pressure achieved at low temperatures is more than 4.5 GPa, which is higher than that of a conventional piston-cylinder cell. The typical sample space at maximum pressure is 1.6 mm in diameter and approximately 0.7 mm in depth, and magnetic measurements such as ac-susceptibility and nuclear magnetic resonance can be performed using a miniature coil. All the components of the indenter cell are made of nonmagnetic materials that have enough thermal conductivity for low-temperature experiments using a He-3/He-4 dilution refrigerator. Another indenter-type cell designed for a commercial superconducting quantum interference device magnetometer is also reported. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2459512

Transport and magnetic properties of pressure-induced insulating phase in PrFe4P12 Reviewed

Hiroyuki Hidaka, Hisashi Kotegawa, Satoshi Fukushima, Naoki Wada, Tatsuo C. Kobayashi, Hisatomo Harima, Kenji Fujiwara, Daisuke Kikuchi, Hideyuki Sato, Hitoshi Sugawara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 9 ) 2006.9

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

We have studied the physical properties of a pressure-induced insulating phase in PrFe4P12 via Hall effect, P-31-NMR and magnetization measurements under quasi-hydrostatic pressure. In the Hall effect measurement, a decrease in the number of hole carriers due to the metal-insulator (M-I) transition is confirmed, indicating a band insulating state. The P-31-NMR spectrum exhibits abrupt broadening and the susceptibility is suppressed markedly owing to the M-I transition, suggesting that an antiferromagnetic ordering occurs in the insulating phase and the M-I transition is of first order. Both spectra corresponding to the metallic and insulating phases are observed simultaneously in a wide temperature range near the M-I transition. This fact reflects the sensitivity of the M-I transition to uniaxial stress, which is confirmed in the resistivity measurement under uniaxial stress.

DOI： 10.1143/JPSJ.75.094709

Pressure-induced superconductivity in CeNiGe3 Reviewed

H Kotegawa, T Miyoshi, K Takeda, S Fukushima, H Hidaka, K Tabata, TC Kobayashi, M Nakashima, A Thamizhavel, R Settai, Y Onuki

PHYSICA B-CONDENSED MATTER 378-80 419 - 420 2006.5

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

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

DOI： 10.1016/j.phys.2006.01.147

Pressure-induced superconductivity in ferromagnet UIr without inversion symmetry Reviewed

TC Kobayashi, S Fukushima, H Hidaka, H Kotegawa, T Akazawa, E Yamamoto, Y Haga, R Settai, Y Onuki

PHYSICA B-CONDENSED MATTER 378-80 355 - 358 2006.5

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

High-pressure AC-susceptibility measurement has been carried out in UIr. Three series of peaks corresponding to the successive ferromagnetic transitions indicate the existence of three ferromagnetic phases FM 1-3. The phase boundary between FM2 and FM3 was not realized in the resistivity measurement. The Meissner effect is observed successfully in the pressure range of 2.63-2.74 GPa where the peak of AC-susceptibility survives. This result indicates that the superconducting phase is embedded in the FM3 phase with the ordered moment less than 0.051 mu(B)/U and adjoins the quantum critical point. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.26

Anisotropic behavior in resistivity of RAgSb2 (R = Ce, La) Reviewed

Y Watanabe, Y Inada, H Hidaka, H Kotegawa, TC Kobayashi, TD Matsuda, D Aoki

PHYSICA B-CONDENSED MATTER 378-80 827 - 828 2006.5

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

CeAgSb2 crystallizes in the tetragonal ZrCuSi2 type structure (P4/nmm), which consists of Sb-Ce, Sb-Ag-Ce, Sb-Sb layers. It shows the peculiar anisotropic ferromagnetic ordering below 9.7 K with a small ordered moment of 0.33 mu B. Its residual resistivity steeply increases above p(c) congruent to 3.3 GPa where the magnetic order disappears. It is expected that the p-f mixing on the peculiar hollow square pillar-like Fermi surface plays an important role in CeAgSb2, while similar Fermi surfaces were not observed in LaAgSb,. We have measured the anisotropy in the electrical resistivity of CexLa1-xAgSb2 to study the p-f mixing effect. Small humps were observed in the temperature dependence of the resistivity in (CeLa1-xAgSb2)-La-x. We expected them the CDW transition. The CDW state coexisted with the ferromagnetic state around x = 0.2. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.305

Evidence for unconventional superconducting fluctuations in heavy-fermion compound CeNi2Ge2 Reviewed

S Kawasaki, T Sada, T Miyoshi, H Kotegawa, H Mukuda, TC Kobayashi, T Fukuhara, K Maezawa, KM Itoh, EE Haller

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 4 ) 2006.4

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

We present evidence for unconventional superconducting fluctuations in a heavy-fermion compound CeNi2Ge2. The temperature dependence of the Ge-73 nuclear-spin-lattice-relaxation rate 1/T-1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than T-FL = 0.4 K, where 1/T1T is constant. The resistance and 1/T1T measured on an as-grown sample decrease below 7(c)(onset) = 0.2 K and T-c(NQR) = 0.1 K, respectively: these are indicative of the onset of superconductivity. However, after annealing the sample to improve its quality. these superconducting signatures disappear. These results are consistent with the emergence of unconventional superconducting fluctuations in close proximity to a quantum critical point from the superconducting to the normal phase in CeNi2Ge2.

DOI： 10.1143/JPSJ.75.043702

Electronic states in a semimetal Ce3Sn7 Reviewed

Y Okuda, MT Suzuki, H Harima, M Nakashima, S Kirita, TC Kobayashi, R Settai, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 4 ) 2006.4

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

We carried out the de Haas-van Alphen (dHvA) measurement and the pressure experiment of the electrical resistivity for an antiferromagnet Ce3Sn7 with the orthorhombic crystal structure. The detected dHvA branches are many in number and their dHvA frequencies are extremely small in magnitude, indicating that Ce3Sn7 is a semimetal. This is consistent with the result of the energy band calculations under the assumption that the 4f electrons of two Ce atoms in the 2(a) site are localized and the 4f electron of one Ce atom in the 4(i) site is itinerant. In the pressure experiment, the Neel temperature of T-N = 5.3 K is found to slightly increase with increasing pressure, becomes maximum around 1 GPa, then decreases steeply with further increasing pressure and most likely becomes zero between 3 and 4GPa. The anti ferromagnetic state is changed into the non-magnetic state under pressure.

DOI： 10.1143/JPSJ.75.044715

Tomonaga-Luttinger liquid in a quasi-one-dimensional S=1 antiferromagnet observed by specific heat measurements Reviewed

M Hagiwara, H Tsujii, CR Rotundu, B Andraka, Y Takano, N Tateiwa, TC Kobayashi, T Suzuki, S Suga

PHYSICAL REVIEW LETTERS 96 ( 14 ) 2006.4

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

Specific-heat experiments on single crystals of the S=1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C9H24N4)(NO2)ClO4 (NTENP) have been performed in magnetic fields applied both parallel and perpendicular to the spin chains. We have found for the parallel field configuration that the magnetic specific heat (C-mag) is proportional to temperature (T) above a critical field H-c, at which the energy gap vanishes, in a temperature region above that of the long-range ordered state. The ratio C-mag/T increases as the magnetic field approaches H-c from above. The data are in good quantitative agreement with the prediction of the c=1 conformal field theory in conjunction with the velocity of the excitations calculated by a numerical diagonalization, providing conclusive evidence for a Tomonaga-Luttinger liquid.

DOI： 10.1103/PhysRevLett.96.147203

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