研究者詳細 - 小林　達生

High Pressure Methods at Low Temperatures and High Magnetic Field 査読

M. I. Eremets, K. Amaya, K. Shimizu, T. C. Kobayashi

Rev. High Pressure Sci. Technol. 7 469 - 474 1997年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：The Japan Society of High Pressure Science and Technology

High-pressure cells which can be used in experiments at low temperatures and high magnetic fields are considered. New constructions of piston-cylinder, diamond anvil and other cells are presented. The recent development of a technique for resistance measurements in the megabar region above 150 GPa are presented. For the first time electrical measurements in the DAC with typical megabar anvils were performed with a sample of diameter 20 μm. The metallization of sulfur at 100 GPa, CsI at 120 GPa was achieved. Simultaneously, with electrical measurements the Raman spectra of sulfur were studied up to 100 GPa.

DOI： 10.4131/jshpreview.7.469

その他リンク： https://jlc.jst.go.jp/DN/JALC/00115529663?from=CiNii

Pressure Induced Superconductivity in Some Simple Systems 査読

K. Amaya, K. Shimizu, N. Takeshita, S. Kometani, M. I. Eremets, A. Onodera, T. C. Kobayashi, T. Mizutani, M. Ishizuka, S. Endo, M. Takai, N. Hamaya, I. Shirotani

Rev. High Pressure Sci. Technol. 7 688 - 693 1997年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：The Japan Society of High Pressure Science and Technology

Experimental techniques on production of ultra-high pressure at very low temperature, electrical resistance and magnetization measurement are developed for the purpose of searching for pressure-induced superconductivity in some simple systems. Previous results of pressure induced superconductivity of I, Br, Ca, SnI₄ and C₆I₄O₂ are reviewed and remaining problems are discussed shortly. Recent findings of metallization and superconductivity of O and S are also reported.

DOI： 10.4131/jshpreview.7.688

その他リンク： https://jlc.jst.go.jp/DN/JALC/00115566545?from=CiNii

Magnetic properties of 1,5-dimethyl-6-oxoverdazyl radical crystal. Observation of a spin-Peierls transition in 3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl radical, p-CyDOV 査読

Kazuo Mukai, Naoki Wada, Javad, B. Jamali, Norio Achiwa, Yasuo Narumi, Koichi Kindo, Tatsuo Kobayashi, Kiichi Amaya

Molecular Crystals and Liquid Crystals 305 499 - 508 1997年

Magnetic properties of 1,5-dimethyl-6-oxoverdazyl radical crystals. Observation of a spin-Peierls transition in 3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl radical, p-CyDOV 査読

K Mukai, N Wada, JB Jamali, N Achiwa, Y Narumi, K Kindo, T Kobayashi, K Amaya

CHEMICAL PHYSICS LETTERS 257 ( 5-6 ) 538 - 544 1996年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Magnetic susceptibilities of 5 kinds of 3-(4-R-phenyl)-1,5-dimethyl-6-oxoverdazyl radicals (PDOV (R=H), p-MDOV (R-CH3O), p-MeDOV (R=CH3), p-CyDOV (R=CN), and p-NDOV (R=NO2)) have been measured in the temperature range of 4.2-300 K. The susceptibilities of PDOV, p-MDOV, and p-MeDOV can be explained by an antiferromagnetic Heisenberg alternating chain model. The susceptibility of p-CyDOV shows a broad maximum at 54 K, and decreases abruptly at 15 K, suggesting a spin-Peierls transition, High-field magnetization data (H=0-35 T) which provide a clear evidence for a spin-Peierls transition were reported.

DOI： 10.1016/0009-2614(96)00577-5

Web of Science

Superconductivity of Calcium under High Pressures 査読

S. Okada, K. Shimizu, T. C. Kobayashi, K. Amaya, S. Endo

J. Phys. Soc. Jpn 65 ( 7 ) 1924 - 1926 1996年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

Electrical resistance of Ca is measured under pressures up to 150 GPa and at temperatures down to 0.05 K. Superconductivity is observed at temperatures below 3 K under pressures above 85 GPa. The superconducting transition temperature increases linearly with increasing pressure and reaches about 15 K at 150 GPa.

DOI： 10.1143/JPSJ.65.1924

High field heat capacities of some singlet ground state systems at very low temperatures 査読

T. C. Kobayashi, A. Koda, K. Amaya

Physica B: Condensed Matter 216 ( 3-4 ) 304 - 306 1996年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier

Several aspects of high field heat capacity observed in different types of singlet ground state system are discussed. The ground state energy gap and its magnetic field dependence are also studied in the Haldane gap compounds NENP, NINO and TMNIN. The origin of the observed minimum gap in applied magnetic field is discussed. In the spin-Peierls compound CuGeO3, the energy gap of the Cu2+ spin system in the dimerized phase and the gapless state in the high-field magnetic phase are confirmed.

DOI： 10.1016/0921-4526(95)00500-5

Scopus

Low Temperature Thermal and Magnetic Properties of Cu-Doped Haldane Gap Antiferromagnet NENP 査読

Kobayashi Tatsuo C., Honda Hajime, Koda Akihiro, Amaya Kiichi

Journal of the Physical Society of Japan 64 ( 7 ) 2609 - 2613 1995年7月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

Effects of Cu-impurity are studied by heat capacity and susceptibility measurements down to 30 mK on the Haldane-gap antiferromagnet Ni(C2H8N2)2NO2(ClO4) (NENP). We have observed the characteristic heat capacity and susceptibility which show contributions from free spins of the Cu2+-impurities with S=1/2 and the fractional spin S=1/2 states at the ends of the Ni2+(S=1)-chain adjacent to the Cu2+-impurities. The present results are explained completely by the phenomenological Hamiltonian for a trimmer of S=1/2 proposed by the ESR study on this system.

DOI： 10.1143/JPSJ.64.2609

その他リンク： https://jlc.jst.go.jp/DN/JALC/00034670958?from=CiNii

Heat capacities of one-dimensional Heisenberg antiferromagnets under high magnetic fields 査読

T. C. Kobayashi, A. Koda, H. Honda, C. U. Hong, K. Amaya, T. Asano, Y. Ajiro, M. Mekata, T. Yosida

Physica B: Physics of Condensed Matter 211 ( 1-4 ) 205 - 207 1995年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

Heat capacity measurements under magnetic fields are carried out on one-dimensional Heisenberg antiferromagnets, a spin-Peierls (SP) and Haldane gap system. In the SP system CuGeO3, the jump in the heat capacity corresponding to SP transition is observed under fields up to 13 T. The obtained field-temperature phase diagram is in good agreement with the previous results of magnetic measurements. The heat capacity follows the exponential temperature dependence at low temperatures under zero field, while it approaches T3-dependence under external field. The heat capacity of Haldane gap system NINO is almost the same as that of NENP. The energy gap at and above Hc is caused by the existence of the transverse moment. © 1995.

DOI： 10.1016/0921-4526(94)00986-6

Scopus

NMR study of strongly correlated electron systems 査読

Y. Kitaoka, H. Tou, G. -q. Zheng, K. Ishida, K. Asayama, T. C. Kobayashi, A. Kohda, N. Takeshita, K. Amaya, Y. Onuki, G. Geibel, C. Schank, F. Steglich

PHYSICA B-CONDENSED MATTER 206 ( 1-4 ) 55 - 61 1995年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Various types of ground states in strongly correlated electron systems have been systematically investigated by means of NMR/NQR at low temperatures under high magnetic field and pressure. We focus on two well-known heavy-electron families, CeCu2X2 (X = Si and Ge) (Ce(122)) and UM2Al3 (M = Ni and Pd) (U(123)). The Cu NQR experiments on CeCu2X2 under high pressure indicate that the physical property of CeCu2Ge2 at high pressure, i.e. above the transition at 7.6GPa from antiferromagnetic (AF) to superconductivity, are clearly related to that of CeCu2Si2 at ambient pressure. In addition to the H-T phase diagram established below 7 T, NMR and specific heat experiments on polycrystal CeCu2.05Si2 have revealed the presence of a new phase above 7 T. In a high-quality polycrystal of UPd2Al3 with a record high-T-c of 2 K at ambient pressure and the narrowest AI NQR line width, the nuclear-spin lattice relaxation rate, (27)(1/T-1) measured in zero field has been found to obey the T-3 law down to 0.13 K, giving strong evidence that the energy gap vanishes along lines on the Fermi surface. Thus it seems that all heavy-electron superconductors exhibit lines of zero gap, regardless of their different magnetic properties.

DOI： 10.1016/0921-4526(94)00365-3

Web of Science

その他リンク： http://orcid.org/0000-0001-5081-2777

Heat capacity anomaly of CeCu2.05Si2 under magnetic fields 査読

T. C. Kobayashi, A. Koda, H. Honda, K. Amaya, Y. Kitaoka, K. Asayama, C. Geibel, F. Steglich

PHYSICA B-CONDENSED MATTER 206 600 - 602 1995年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Heat capacity measurements of CeCu2.05Si2 have been carried out at temperatures down to 0.1 K under magnetic field up to 13 T. The heat capacity divided by temperature C/T has revealed as a characteristic feature that the peak of C/T shifts down to around 0.5 K with increasing field up to 7 T, whereafter it shifts up again to around 0.6 K at 13 T. In the first case, a peak appears around the phase boundary (labeled A) first found in NMR and magnetoresistance. Most remarkably, in the latter case, the peak coincides with the new phase boundary (labeled B) identified recently by elastic constant and thermal expansion measurements.

Web of Science

Low Temperature Thermal and Magnetic Properties of Haldane-Gap Antiferromagnet TMNIN 査読

Kobayashi Tatsuo, Kohda Akihiro, Amaya Kiichi, Ito Masakazu, Deguchi Hiroyuki, Takeda Kazuyoshi, Asano Takayuki, Ajiro Yoshitami, Mekata Mamoru

J Phys Soc Jpn 63 ( 5 ) 1961 - 1966 1994年5月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

Heat capacity and susceptibility measurements are performed downto 70 mK under magnetic fields in the Haldane-gap antiferromagnet(CH3)4NNi(NO2)3 (TMNIN). We have observedno magnetic long range order within our experimental range ofthe temperature down to 70 mK and the magnetic field up to7 T. The heat capacity reflects the field dependence of theenergy gap and show a broad anomaly above a critical fieldH C, which has been also observed in NENP. In theadiabatic magnetization measurement, the spin temperature showsa minimum around H C. These results are interpreted asincreasing of the energy gap above H C which maysuppress the expected long-range-ordering.

DOI： 10.1143/JPSJ.63.1961

Heat Capacities of Haldane-Gap Antiferromagnet NENP in Magnetic Field 査読

Kobayashi Tatsuo, Tabuchi Yoshitaka, Amaya Kiichi, Ajiro Yoshitami, Yosida Taturu, Date Muneyuki

Journal of the Physical Society of Japan 61 ( 5 ) 1772 - 1776 1992年

記述言語：英語出版者・発行元：THE PHYSICAL SOCIETY OF JAPAN

Heat capacity measurements of the quasi one-dimensional S=1 antiferromagnet Ni(C₂H₈N₂)₂NO₂(ClO₄) are performed in static magnetic fields up to 13 T. Applying a magnetic field, a broad anomaly appears below 5 K, which reflects the gap energy between the nonmagnetic ground state singlet and the excited states. The field-dependence of the energy gap estimated from the measured heat capacities gives the critical field values close to those obtained in high-field-magnetization measurements and non-zero gap remaining at the critical field. Within our experimental range of temperature and magnetic field, we have not observed any sharp peaks corresponding to the expected three dimensional magnetic long range ordering.

DOI： 10.1143/JPSJ.61.1772

Nuclear Spin-Lattice Relaxation of 139La in Superconducting (La1-xSrx)2CuO4 査読

Kobayashi Tatsuo, Wada Shinji, Kitaoka Yoshio, Asayama Kunisuke

J Phys Soc Jpn 58 ( 8 ) 2662 - 2664 1989年8月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

Nuclear spin-lattice relaxation times $T_{1}$ of 139La in high-$T_{\text{C } }$ superconductor (La1-xSrx)2CuO4 ($x{=}0.075$, 0.10) have been measured in zero field. $T_{1}^{-1}$ in the superconducting state decreases rapidly, indicating a superconducting energy gap formation, but no signs of $T_{1}^{-1}$ enhancement are observed just below $T_{\text{C } }$. $T_{1}^{-1}$ in the normal state shows slightly stronger temperature dependence than that expected from the Korringa relation ($T_{1}T$${=}$const.) observed in a highly Sr-doped, nonsuperconducting compound with $x{=}0.15$.

DOI： 10.1143/JPSJ.58.2662

Existence of the Minimum Coefficient in Temperature Linear Term of Heat Capacity in Superconducting (La1-xBax)2CuO4 査読

Kobayashi Tatsuo, Kumayasu Satoshi, Amaya Kiichi, Ishida Kenji, Kitaoka Yoshio, Asayama Kunisuke

Journal of the Physical Society of Japan 57 ( 7 ) 2261 - 2263 1988年7月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

In high-$T_{\text{c } }$ superconductors (La1-xMx)2CuO4 (M$=$Ba, Sr), it has been reported that the heat capacity has a nonzero coefficient $\gamma$ in the temperature linear term. We investigated the detailed dependence of $\gamma$ on Ba doping. It was confirmed that $\gamma$ becomes zero for undoped La2CuO4. With increasing Ba concentration $x$, $\gamma$ increases markedly up to $x{=}0.02$ where the magnetic order almost disappears, while it decreases as superconductivity starts to appear and then has a minimum around $x{=}0.04$. With further increasing $x$, $\gamma$ increases again. These results may be due to a combined effect of two different contributions to $\gamma$.

DOI： 10.1143/JPSJ.57.2261