研究者詳細 - 小林　達生

論文 - 小林　達生

分割表示 >> ／全件表示 217 件中 1 - 217 件目

Structural and Superconducting Properties of Bi₂Rh₃(Se_1–xS_x)₂ (x = 0–1.0) 査読

Zhiyan Zhang, Wanli Pan, Masaki Utsumi, Yuki Yamamoto, Hidenori Goto, Ryusuke Kondo, Takayoshi Yokoya, Ryota Goban, Tomoki Higashikawa, Ritsuko Eguchi, Yasuhiro Takabayashi, Koichi Hayashi, Hirofumi Ishii, Tatsuo C. Kobayashi, Yoshihiro Kubozono

Inorganic Chemistry 63 ( 45 ) 21531 - 21540 2024年10月

Ferrimagnetic structure in the high-pressure phase of α−Mn 査読

Shingo Araki, Kaisei Iwamoto, Kazuto Akiba, Tatsuo C. Kobayashi, Koji Munakata, Koji Kaneko, Toyotaka Osakabe

Physical Review B 2024年9月

Realization of nodal-ring semimetal in pressurized black phosphorus 査読

Kazuto Akiba, Yuichi Akahama, Masashi Tokunaga, Tatsuo C. Kobayashi

Physical Review B 109 ( 20 ) 2024年5月

Zero-Field NMR of α-Mn up to 5GPa 査読

Go Fujita, Fumiya Kawanabe, Hideto Fukazawa, Tetsuo Ohama, Yoh Kohori, Kentaro Kitagawa, Kaisei Iwamoto, Shingo Araki, Tatsuo C. Kobayashi

Journal of the Physical Society of Japan 93 ( 2 ) 2024年2月

掲載種別：研究論文（学術雑誌）

We performed zero-field nuclear magnetic resonance (ZF NMR) measurements of the antiferromagnetic and pressure-induced magnetically ordered phases of α-Mn at high pressures using a piston cylinder cell and an opposed-anvil high-pressure cell. We found that 55Mn internal magnetic fields disappeared discontinuously at 4.2–4.3 GPa. This suggests a first-order phase transition.

DOI： 10.7566/JPSJ.93.023707

Pressure Dependence of the Structural and Superconducting Properties of the Bi-Based Superconductor Bi₂Pd₃Se₂ 査読

Zhiyan Zhang, Mitsuki Ikeda, Masaki Utsumi, Yuki Yamamoto, Hidenori Goto, Ritsuko Eguchi, Yen-Fa Liao, Hirofumi Ishii, Yasuhiro Takabayashi, Koichi Hayashi, Ryusuke Kondo, Tatsuo C. Kobayashi, Yoshihiro Kubozono

Inorganic Chemistry 63 ( 5 ) 2553 - 2561 2024年1月

Superconductivity in a ferroelectric-like topological semimetal SrAuBi 査読

Hidefumi Takahashi, Tomohiro Sasaki, Akitoshi Nakano, Kazuto Akiba, Masayuki Takahashi, Alex H. Mayo, Masaho Onose, Tatsuo C. Kobayashi, Shintaro Ishiwata

npj Quantum Materials 8 ( 1 ) 2023年12月

掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Science and Business Media LLC

Abstract

Given the rarity of metallic systems that exhibit ferroelectric-like transitions, it is apparently challenging to find a system that simultaneously possesses superconductivity and ferroelectric-like structural instability. Here, we report the observation of superconductivity at 2.4 K in a layered semimetal SrAuBi characterized by strong spin–orbit coupling (SOC) and ferroelectric-like lattice distortion. Single crystals of SrAuBi have been successfully synthesized and found to show a polar-nonpolar structure transition at 214 K, which is associated with the buckling of Au-Bi honeycomb lattice. On the basis of the band calculations considering SOC, we found significant Rashba-type spin splitting and symmetry-protected multiple Dirac points near the Fermi level. We believe that this discovery opens up new possibilities of pursuing exotic superconducting states associated with the semimetallic band structure without space inversion symmetry and the topological surface state with the strong SOC.

DOI： 10.1038/s41535-023-00612-4

その他リンク： https://www.nature.com/articles/s41535-023-00612-4

Phonon-mediated superconductivity in the Sb square-net compound LaCuSb₂ 査読

Kazuto Akiba, Tatsuo C. Kobayashi

Phys. Rev. B 107 245117 2023年6月

NMR Study of α-Mn Exhibiting Anomalous Hall Effect under High Pressure 査読

H. Fukazawa, G. Fujita, N. Shioda, T. Ohama, Y. Kohori, K. Iwamoto, S. Araki, T. C. Kobayashi

Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 2023年5月

Effect of High Pressure on the Electrical Resistivity of Electric Toroidal Ordering Candidate Ca₅Ir₃O₁₂ 査読

Kazuto Akiba, Tatsuo C. Kobayashi, Momoka Hayashida, Kazuyuki Matsuhira

Journal of the Physical Society of Japan 92 ( 3 ) 2023年3月

Superconductivity in a Magnetic Rashba Semimetal EuAuBi 査読

Hidefumi Takahashi, Kazuto Akiba, Masayuki Takahashi, Alex H. Mayo, Masayuki Ochi, Tatsuo C. Kobayashi, Shintaro Ishiwata

Journal of the Physical Society of Japan 92 ( 1 ) 2023年1月

Site Split of Antiferromagnetic α-Mn Revealed by ⁵⁵Mn Nuclear Magnetic Resonance 査読

Masahiro Manago, Gaku Motoyama, Shijo Nishigori, Kenji Fujiwara, Katsuki Kinjo, Shunsaku Kitagawa, Kenji Ishida, Kazuto Akiba, Shingo Araki, Tatsuo C. Kobayashi, Hisatomo Harima

Journal of the Physical Society of Japan 91 ( 11 ) 2022年11月

Observation of superconductivity and its enhancement at the charge density wave critical point in LaAgSb2 査読

Kazuto Akiba, Nobuaki Umeshita, Tatsuo C. Kobayashi

PHYSICAL REVIEW B 106 ( 16 ) 2022年10月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We discover superconductivity (SC) in LaAgSb2 at ambient pressure and its close correlation with a charge density wave (CDW) under pressure. The superconducting transition temperature (Tc) exhibits a sharp peak at a CDW critical pressure of 3.2 GPa. We demonstrate that the carriers inhabiting the Sb-square net are crucial not only in the formation of CDW but also in SC for their relatively strong electron-phonon coupling (EPC). Furthermore, theoretical EPC strength in pristine LaAgSb2 cannot explain the observed peak with Tc - 1 K, which indicates that an additional mechanism reinforces SC only around the CDW critical pressure.

DOI： 10.1103/PhysRevB.106.L161113

Solid and Liquid Oxygen under Ultrahigh Magnetic Fields 査読

Toshihiro Nomura, Yasuhiro H. Matsuda, Tatsuo C. Kobayashi

Oxygen 2 ( 2 ) 152 - 163 2022年5月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MDPI AG

Oxygen is a unique molecule that possesses a spin quantum number S=1. In the condensed phases of oxygen, the delicate balance between the antiferromagnetic interaction and van der Waals force results in the various phases with different crystal structures. By applying ultrahigh magnetic fields, the antiferromagnetic coupling between O2 molecules breaks, and novel high-field phases can appear. We have investigated the physical properties of condensed oxygen under ultrahigh magnetic fields and have found that the stable crystal structure of solid oxygen changes around 100 T. Even in liquid oxygen, we observed a strong acoustic attenuation, which indicates the fluctuation of local molecular arrangements. These results demonstrate that magnetic fields can modulate the packing structure of oxygen through spin-lattice coupling. Our study implies the possibility of controlling oxygen-related (bio-)chemical processes by using an external magnetic field.

DOI： 10.3390/oxygen2020013

Magnetotransport studies of the Sb square-net compound LaAgSb2 under high pressure and rotating magnetic fields 査読

Kazuto Akiba, Nobuaki Umeshita, Tatsuo C. Kobayashi

Physical Review B 105 ( 3 ) 2022年1月

Physical properties of liquid oxygen under ultrahigh magnetic fields 査読

T. Nomura, A. Ikeda, M. Gen, A. Matsuo, K. Kindo, Y. Kohama, Y. H. Matsuda, S. Zherlitsyn, J. Wosnitza, H. Tsuda, T. C. Kobayashi

Physical Review B 104 ( 22 ) 2021年12月

Spin-gap formation due to spin-Peierls instability in π-orbital-ordered NaO2 査読国際誌

Mizuki Miyajima, Fahmi Astuti, Takahito Fukuda, Masashi Kodani, Shinsuke Iida, Shinichiro Asai, Akira Matsuo, Takatsugu Masuda, Koichi Kindo, Takumi Hasegawa, Tatsuo C. Kobayashi, Takehito Nakano, Isao Watanabe, Takashi Kambe

Physical Review B 104 ( 14 ) 2021年10月

Successive destruction of charge density wave states by pressure in LaAgSb2 査読

Kazuto Akiba, Hiroaki Nishimori, Nobuaki Umeshita, Tatsuo C. Kobayashi

Physical Review B 103 ( 8 ) 2021年2月

Domain Control by Adjusting Anisotropic Stress in Pyrochlore Oxide Cd2Re2O7 査読

Satoshi Tajima, Daigorou Hirai, Yuto Kinoshita, Masashi Tokunaga, Kazuto Akiba, Tatsuo C. Kobayashi, Hishiro T. Hirose, Zenji Hiroi

Journal of the Physical Society of Japan 89 ( 11 ) 114711 - 114711 2020年11月

Anomalous Hall effect triggered by pressure-induced magnetic phase transition in α -Mn 査読

Kazuto Akiba, Kaisei Iwamoto, Takaaki Sato, Shingo Araki, Tatsuo C. Kobayashi

Physical Review Research 2 ( 4 ) 2020年10月

Two Qualitatively Different Superconducting Phases under High Pressure in Single-Crystalline CeNiGe3 査読

Shunsaku Kitagawa, Shingo Araki, Tatsuo C. Kobayashi, Yoichi Ikeda

Journal of the Physical Society of Japan 89 ( 6 ) 063702 - 063702 2020年6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：Japan Society of Applied Physics

We have measured the temperature dependence of resistivity in single-crystalline CeNiGe3 under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase T-N1 = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at similar to 3.0GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at similar to 6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field mu H-0(c2) and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds.

DOI： 10.7566/jpsj.89.063702

Magnetotransport properties of tellurium under extreme conditions 査読

Kazuto Akiba, Kaya Kobayashi, Tatsuo C. Kobayashi, Ryo Koezuka, Atsushi Miyake, Jun Gouchi, Yoshiya Uwatoko, Masashi Tokunaga

Physical Review B 101 ( 24 ) 2020年6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：American Physical Society (APS)

This study investigates the transport properties of a chiral elemental semiconductor tellurium (Te) under magnetic fields and pressure. Application of hydrostatic pressure reduces the resistivity of Te, while its temperature dependence remains semiconducting up to 4 GPa, contrary to recent theoretical and experimental studies. Application of higher pressure causes structural as well as semiconductor-metal transitions. The resulting metallic phase above 4 GPa exhibits superconductivity at 2 K along with a noticeable linear magnetoresistance effect. On the other hand, at ambient pressure, we identified metallic surface states on the as-cleaved (10 (1) over bar0) surfaces of Te. The nature of these metallic surface states has been systematically studied by analyzing quantum oscillations observed in high magnetic fields. We clarify that a well-defined metallic surface state exists not only on chemically etched samples that were previously reported, but also on as-cleaved ones.

DOI： 10.1103/physrevb.101.245111

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.101.245111/fulltext

Variation in Superconducting Symmetry Against Pressure on Noncentrosymmetric Superconductor Cd2Re2O7 Revealed by 185/187Re Nuclear Quadrupole Resonance 査読

Shunsaku Kitagawa, Kenji Ishida, Tatsuo C. Kobayashi, Yasuhito Matsubayashi, Daigorou Hirai, Zenji Hiroi

Journal of the Physical Society of Japan 89 ( 5 ) 053701 - 053701 2020年5月

Pressure-Temperature Phase Diagram of alpha-Mn 査読国際誌

Takaaki Sato, Kazuto Akiba, Shingo Araki, Tatsuo C. Kobayashi

Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019) 30 011030-1 - 011030-6 2020年3月

Helimagnetic Structure and Heavy-Fermion-Like Behavior in the Vicinity of the Quantum Critical Point in Mn3P 査読

Hisashi Kotegawa, Masaaki Matsuda, Feng Ye, Yuki Tani, Kohei Uda, Yoshiki Kuwata, Hideki Tou, Eiichi Matsuoka, Hitoshi Sugawara, Takahiro Sakurai, Hitoshi Ohta, Hisatomo Harima, Keiki Takeda, Junichi Hayashi, Shingo Araki, Tatsuo C. Kobayashi

Physical Review Letters 124 ( 8 ) 2020年2月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Physical Society (APS)

Antiferromagnet Mn3P with Neel temperature T-N = 30 K is composed of Mn tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at similar to 1.6 GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn3P, which is most likely effected by the underlying frustration effect.

DOI： 10.1103/physrevlett.124.087202

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.124.087202/fulltext

High magnetic field x-ray diffraction study of the α phase of solid oxygen: Absence of giant magnetostriction 査読

Yasuhiro H. Matsuda, Ayumi Shimizu, Akihiko Ikeda, Toshihiro Nomura, Takeshi Yajima, Toshiya Inami, Kohki Takahashi, Tatsuo C. Kobayashi

Physical Review B 100 ( 21 ) 2019年12月

Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCu2Si2 versus YbRh2Si2 査読

M. Smidman, O. Stockert, J. Arndt, G. M. Pang, L. Jiao, H. Q. Yuan, H. A. Vieyra, S. Kitagawa, K. Ishida, K. Fujiwara, T. C. Kobayashi, E. Schuberth, M. Tippmann, L. Steinke, S. Lausberg, A. Steppke, M. Brando, H. Pfau, U. Stockert, P. Sun, S. Friedemann, S. Wirth, C. Krellner, S. Kirchner, E. M. Nica, R. Yu, Q. Si, F. Steglich

Philosophical Magazine 98 ( 32 ) 2930 - 2963 2018年11月

Pyrochlore Oxide Superconductor Cd2Re2O7Revisited 査読

Zenji Hiroi, Jun-ichi Yamaura, Tatsuo C. Kobayashi, Yasuhito Matsubayashi, Daigorou Hirai

Journal of the Physical Society of Japan 87 ( 2 ) 024702 - 024702 2018年2月

Magnetostriction studies up to megagauss fields using fiber Bragg grating technique

Akihiko Ikeda, Yasuhiro H. Matsuda, Daisuke Nakamura, Shojiro Takeyama, Hiroshi Tsuda, Kazuya Nomura, Ayumi Shimizu, Akira Matsuo, Toshihiro Nomura, Tatsuo C. Kobayashi, Takeshi Yajima, Hajime Ishikawa, Zenji Hiroi, Masahiko Isobe, Touru Yamauchi, Keisuke Sato

2018 16TH INTERNATIONAL CONFERENCE ON MEGAGAUSS MAGNETIC FIELD GENERATION AND RELATED TOPICS (MEGAGAUSS) 98 - 106 2018年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

We here report magnetostriction measurements under pulsed megagauss fields using a high-speed 100 MHz strain monitoring system devised using fiber Bragg grating (FBG) technique with optical filter method. The optical filter method is a detection scheme of the strain of FBG, where the changing Bragg wavelength of the FBG reflection is converted to the intensity of reflected light to enable the 100 MHz measurement. In order to show the usefulness and reliability of the method, we report the measurements for solid oxygen, spin-controlled crystal, and volborthite, a deformed Kagome quantum spin lattice, using static magnetic fields up to 7 T and non-destructive millisecond pulse magnets up to 50 T. Then, we show the application of the method for the magnetostriction measurements of CaV4O9, a two-dimensional antiferromagnet with spin-halves, and LaCoO3, an anomalous spin-crossover oxide, in the megagauss fields.

Pressure-Induced Superconductivity from Doping-Induced Antiferromagnetic Phase of 112-type Ca1−xLaxFeAs2 査読

Shunsaku Kitagawa, Taishi Sekiya, Yo Fujiyoshi, Shingo Araki, Tatsuo C. Kobayashi, Naoki Nishimoto, Tasuku Mizukami, Satoshi Ioka, Kazunori Fujimura, Kazutaka Kudo, Minoru Nohara

Journal of the Physical Society of Japan 86 ( 11 ) 113705 - 113705 2017年11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：Physical Society of Japan

The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca1-xLaxFeAs2 were studied, and the in-plane electrical resistivity rho(ab) was measured with an indenter-type pressure cell. The AFM phase transition temperatures of T-N = 47, 63, and 63 K at ambient pressure for x = 0.18, 0.21, and 0.26 was suppressed by applying pressure P, with superconductivity emerging at critical pressures of P-c similar or equal to 0, 1.5, and 3.4 GPa, respectively. Correspondingly, the slope of T-N against P decreased as dT(N)/P similar or equal to -15 and -2K/GPa for x = 0.21 and 0.26, respectively. Thus, although the AFM phase was stabilized with La doping x, the AFM phase was suppressed by pressure, and superconductivity eventually emerged.

DOI： 10.7566/jpsj.86.113705

H−T phase diagram of solid oxygen 査読

T. Nomura, Y. H. Matsuda, T. C. Kobayashi

Physical Review B 96 ( 5 ) 2017年8月

alpha-beta and beta-gamma phase boundaries of solid oxygen observed by adiabatic magnetocaloric effect 査読

Toshihiro Nomura, Yoshimitsu Kohama, Yasuhiro H. Matsuda, Koichi Kindo, Tatsuo C. Kobayashi

Phys Rev B 5 104420 2017年3月

Successive spatial symmetry breaking under high pressure in the spin-orbit-coupled metal Cd2Re2O7 査読

Jun-ichi Yamaura, Keiki Takeda, Yoichi Ikeda, Naohisa Hirao, Yasuo Ohishi, Tatsuo C. Kobayashi, Zenji Hiroi

PHYSICAL REVIEW B 95 ( 2 ) 163 - 170 2017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：AMER PHYSICAL SOC

The 5d-transition-metal pyrochlore oxide Cd2Re2O7, which was recently suggested to be a prototype of the spin-orbit-coupled metal [Phys. Rev. Lett. 115, 026401 (2015)], exhibits an inversion-symmetry-breaking (ISB) transition at 200 K and a subsequent superconductivity below 1 K at ambient pressure. We study the crystal structure at high pressures up to 5 GPa by means of synchrotron x-ray powder diffraction. A rich structural phase diagram is obtained, which contains at least seven phases, and is almost consistent with the electronic phase diagram determined by previous resistivity measurements. Interestingly, the ISB transition vanishes at similar to 4 GPa where the enhancement of the upper critical field was observed in resistivity. Moreover, it is shown that the point groups at 8 K, probably kept in the superconducting phases, sequentially transform into piezoelectric, ferroelectric, and centrosymmetric structures on the application of pressure.

DOI： 10.1103/PhysRevB.95.020102

Chemical analysis of superconducting phase in K-doped picene 査読

Takashi Kambe, Saki Nishiyama, Huyen L. T. Nguyen, Takahiro Terao, Masanari Izumi, Yusuke Sakai, Lu Zheng, Hidenori Goto, Yugo Itoh, Taiki Onji, Tatsuo C. Kobayashi, Hisako Sugino, Shin Gohda, Hideki Okamoto, Yoshihiro Kubozono

JOURNAL OF PHYSICS-CONDENSED MATTER 28 ( 44 ) 2016年11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：IOP PUBLISHING LTD

Potassium-doped picene (K(3.0)picene) with a superconducting transition temperature (TC) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The TC showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

DOI： 10.1088/0953-8984/28/44/444001

Irreversible Heating Measurement with Microsecond Pulse Magnet: Example of the alpha-theta Phase Transition of Solid Oxygen 査読

Toshihiro Nomura, Yasuhiro H. Matsuda, Shojiro Takeyama, Tatsuo C. Kobayashi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 85 ( 9 ) 2016年9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：PHYSICAL SOC JAPAN

Dissipation inevitably occurs in first-order phase transitions, leading to irreversible heating. Conversely, the irreversible heating effect may indicate the occurrence of the first-order phase transition. We measured the temperature change at the magnetic-field-induced alpha-theta phase transition of solid oxygen. A significant temperature increase from 13 to 37 K, amounting to 700 J/mol, due to irreversible heating was observed at the first-order phase transition. We argue that the hysteresis loss of the magnetization curve and the dissipative structural transformation account for the irreversible heating. The measurement of irreversible heating can be utilized to detect the first-order phase transition in combination with an ultrahigh magnetic fields generated in a time of mu s order.

DOI： 10.7566/JPSJ.85.094601

Characteristic Fermi surfaces and charge density wave in SrAl4 and related compounds with the BaAl4-type tetragonal structure 査読

Ai Nakamura, Taro Uejo, Hisatomo Harima, Shingo Araki, Tatsuo C. Kobayashi, Miho Nakashima, Yasushi Amako, Masato Hedo, Takao Nakama, Yoshichika Onuki

JOURNAL OF ALLOYS AND COMPOUNDS 654 290 - 299 2016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 SCIENCE SA

We succeeded in growing single crystals of SrAl4 and related compounds with the BaAl4-type tetragonal structure by the self-flux method, and measured the electrical resistivity, magnetic susceptibility, Hall coefficient, thermoelectric power, and de Haas-van Alphen (dHvA) effect. A plausible characteristic feature of the charge density wave (CDW) was observed below T-CDW = 243 K in SrAl4. We also studied an effect of pressure on the electronic state in SrAl4 by measuring the electrical resistivity and thermoelectric power. T-CDW is found to decrease with increasing pressure, with a rate of dT(CDW)/dP = -12.5 K/GPa. To clarify the Fermi surface nesting, we studied the Fermi surface in SrAl4, which is found to be different from the Fermi surfaces of the similar compounds SrGa4, BaGa4, and BaAl4 without CDW. The Fermi surfaces in these compounds were determined from the dHvA experiments, together with the energy band calculations. (C) 2015 Published by Elsevier B.V.

DOI： 10.1016/j.jallcom.2015.08.193

Hall Effect in CeIn3 under High Pressure 査読

Shingo Araki, Taiki Onji, Shunsaku Kitagawa, Tatsuo C. Kobayashi, Takashi Kambe

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 ( 12 ) 123702-1-123702-4 2015年12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：PHYSICAL SOC JAPAN

The temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* similar to 80K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2K even near the critical pressure where antiferromagnetic ordering disappears.

DOI： 10.7566/JPSJ.84.123702

Suppression of Nonmagnetic Insulating State by Application of Pressure in Mineral Tetrahedrite Cu12Sb4S13 査読

Shunsaku Kitagawa, Taishi Sekiya, Shingo Araki, Tatsuo C. Kobayashi, Kenji Ishida, Takashi Kambe, Takumi Kimura, Naoki Nishimoto, Kazutaka Kudo, Minoru Nohara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 ( 9 ) 093701-1-093701-4 2015年9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：PHYSICAL SOC JAPAN

The mineral tetrahedrite Cu12Sb4S13 exhibits a first-order metal-insulator transition (MIT) at T-MI = 85K and ambient pressure. We measured the 63Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. Cu-63-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at similar to 1.0 GPa. Two other anomalies are observed in the resistivity measurements, and the pressure-temperature phase diagram of Cu12Sb4S13 is constructed.

DOI： 10.7566/JPSJ.84.093701

Phase boundary of θ phase of solid oxygen in ultrahigh magnetic fields 査読

T. Nomura, Y. H. Matsuda, S. Takeyama, A. Matsuo, K. Kindo, T. C. Kobayashi

Physical Review B - Condensed Matter and Materials Physics 92 ( 6 ) 2015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：American Physical Society

The phase diagram of solid oxygen in the magnetic-field-temperature (B-T) plane is revealed by magnetization and magnetotransmission measurements. The high-field phase of solid oxygen, which we term the θ phase, is induced at the temperature below 42 K. The transition fields at the α-θ and β-θ transitions are almost temperature independent, with the phase boundary being very steep. This phase boundary indicates that the entropy change is very small at the α-θ and β-θ transitions, in contrast to the entropy-driven β-γ transition at zero field. We argue that the θ phase differs from the high-temperature γ phase in terms of entropy
the molecular rotation is inhibited in the θ phase, whereas permitted in the γ phase. This finding consolidates the novelty of the θ phase.

DOI： 10.1103/PhysRevB.92.064109

Emergence of double-dome superconductivity in ammoniated metal-doped FeSe 査読

Masanari Izumi, Lu Zheng, Yusuke Sakai, Hidenori Goto, Masafumi Sakata, Yuki Nakamoto, Huyen L. T. Nguyen, Tomoko Kagayama, Katsuya Shimizu, Shingo Araki, Tatsuo C. Kobayashi, Takashi Kambe, Dachun Gu, Jing Guo, Jing Liu, Yanchun Li, Liling Sun, Kosmas Prassides, Yoshihiro Kubozono

SCIENTIFIC REPORTS 5 9477-1-9477-7 2015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：NATURE PUBLISHING GROUP

The pressure dependence of the superconducting transition temperature (T-c) and unit cell metrics of tetragonal (NH3)(y)Cs0.4FeSe were investigated in high pressures up to 41 GPa. The T-c decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The T-c vs. c plot is compared with those of various (NH3)(y)MxFeSe (M: metal atoms) materials exhibiting different T-c and c, showing that the T-c is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the T-c. No superconductivity was observed down to 4.3 K in (NH3)(y)Cs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the T-c reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, T-c slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

DOI： 10.1038/srep09477

Pressure-Temperature-Field Phase Diagram in the Ferromagnet U3P4 査読

Shingo Araki, Minami Hayashida, Naoto Nishiumi, Hiroki Manabe, Yoichi Ikeda, Tatsuo C. Kobayashi, Keizo Murata, Yoshihiko Inada, Piotr Wisniewski, Dai Aoki, Yoshichika Onuki, Etsuji Yamamoto, Yoshinori Haga

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 ( 2 ) 024705-1-024705-8 2015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：PHYSICAL SOC JAPAN

The pressure-temperature-field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at P-c similar to 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at P-c follows T-5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at P-c may be considered as weakly first-order. Another critical behavior, the huge enhancement of rho(0) observed at P-c, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

DOI： 10.7566/JPSJ.84.024705

Resistance Anomalies Accompanying Crossover from Heavy-Fermion Regime to Intermediate-Valence Regime: A Study of Cu-Ni Substitution and Pressure Effects on CeCu2Si2 査読

Yoichi Ikeda, Yuzo Ito, Shingo Araki, Tatsuo C. Kobayashi, Hideki Yoshizawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 ( 2 ) 024702-1-024702-9 2015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：PHYSICAL SOC JAPAN

We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu1-xNix)(2)Si-2 with x < 0.3, and a pressure (p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu-Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu2Si2, and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence(IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu2Si2, namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T-2-resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x-p phase diagram of Ce(Cu1-xNix)(2)Si-2, we demonstrate that the crossover from the HF regime to the IV regime can be associated with these characteristic anomalies in resistivity.

DOI： 10.7566/JPSJ.84.024702

Characterization of Ferromagnetic Order in CePd2P2 査読

Y. Ikeda, H. Yoshizawa, S. Konishi, S. Araki, T. C. Kobayashi, T. Yokoo, S. Ito

INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS 2014 (SCES2014) 592 012013-1-012013-6 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We examine magnetic ordering in CePd2P2 by neutron-scattering experiment and confirmed a ferromagnetic order at low temperatures. From the neutron-scattering data, the ordered moment is evaluated to be similar to 1.3(3) mu(B) per Ce ion at 3 K and is considered to be parallel to the c-axis. In addition, no evidence of the change in the magnetic structure was observed below T-C within the experimental accuracy. In DC magnetization measurement with an as-grown powder sample and a magnetically aligned sample, a clear magnetic anisotropy in CePd2P2 was observed in both ferromagnetic and paramagnetic phases. To obtain further insight to the large Curie temperature T-C of CePd2P2, we have examined the magnetic properties of GdPd2P2 as a reference material. In DC magnetization measurement, successive magnetic transitions at T-I = 10.6 K and T-II = 7.4 K were observed in GdPd2P2. By comparing the transition temperatures of the Ce and Gd compounds, we argue the origin of the large Curie temperature of CePd2P2.

DOI： 10.1088/1742-6596/592/1/012013

Simultaneous suppression of superconductivity and structural phase transition under pressure in Ca-10(Ir4As8)(Fe2-xIrxAs2)(5) 査読

Shunsaku Kitagawa, Shingo Araki, Tatsuo C. Kobayashi, Hiroyuki Ishii, Kazunori Fujimura, Daisuke Mitsuoka, Kazutaka Kudo, Minoru Nohara

PHYSICAL REVIEW B 90 ( 22 ) 224513-1-224513-4 2014年12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：AMER PHYSICAL SOC

We measured the pressure dependence of in-plane resistivity rho(ab) in the recently discovered iron-based superconductor Ca-10(Ir4As8)(Fe2-xIrxAs2)(5), which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature T-c = 16 K and a structural phase transition temperature T-s similar or equal to 100 K at ambient pressure. T-c and T-s are suppressed on applying pressure and disappear at approximately 0.5 GPa, suggesting a relationship between superconductivity and structure. Ca-10(Ir4As8)(Fe2-xIrxAs2)(5) is a rather rare example in which the superconductivity appears only in a low-temperature ordered phase. The fact that the change in the crystal structure is directly linked with superconductivity suggests that the crystal structure as well as magnetism are important factors governing superconductivity in iron pnictides.

DOI： 10.1103/PhysRevB.90.224513

Role of Valence Fluctuations in the Superconductivity of Ce122 Compounds 査読

H. Yamaoka, Y. Ikeda, I. Jarrige, N. Tsujii, Y. Zekko, Y. Yamamoto, J. Mizuki, J. -F. Lin, N. Hiraoka, H. Ishii, K. -D. Tsuei, T. C. Kobayashi, F. Honda, Y. Onuki

PHYSICAL REVIEW LETTERS 113 ( 8 ) 86403-1-86403-6 2014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：AMER PHYSICAL SOC

Pressure dependence of the Ce valence in CeCu2Ge2 has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20Kusing x-ray absorption spectroscopy in the partial fluorescence yield. Asmooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu1-xNix)(2)Si-2 at 20 K. Avery weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results showno evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.

DOI： 10.1103/PhysRevLett.113.086403

Novel Phase of Solid Oxygen Induced by Ultrahigh Magnetic Fields 査読

T. Nomura, Y. H. Matsuda, S. Takeyama, A. Matsuo, K. Kindo, J. L. Her, T. C. Kobayashi

PHYSICAL REVIEW LETTERS 112 ( 24 ) 247201-1-247201-5 2014年6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：AMER PHYSICAL SOC

Magnetization measurements and magnetotransmission spectroscopy of the solid oxygen alpha phase were performed in ultrahigh magnetic fields of up to 193 T. An abrupt increase in magnetization with large hysteresis was observed when pulsed magnetic fields greater than 120 T were applied. Moreover, the transmission of light significantly increased in the visible range. These experimental findings indicate that a first-order phase transition occurs in solid oxygen in ultrahigh magnetic fields, and that it is not just a magnetic transition. Considering the molecular rearrangement mechanism found in the O-2-O-2 dimer system, we conclude that the observed field-induced transition is caused by the antiferromagnetic phase collapsing and a change in the crystal structure.

DOI： 10.1103/PhysRevLett.112.247201

Orbital Zeeman Effect of Liquid Oxygen in High Magnetic Fields 査読

Toshihiro Nomura, Yasuhiro H. Matsuda, Shojiro Takeyama, Akira Matsuo, Koichi Kindo, Tatsuo C. Kobayashi

Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013) 2014年6月

Superconducting phases in (NH3)(y)MxFeSe1-zTez (M = Li, Na, and Ca) 査読

Yusuke Sakai, Lu Zheng, Masanari Izumi, Kazuya Teranishi, Ritsuko Eguchi, Hidenori Goto, Taiki Onji, Shingo Araki, Tatsuo C. Kobayashi, Yoshihiro Kubozono

PHYSICAL REVIEW B 89 ( 14 ) 144509-1-144509-6 2014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：AMER PHYSICAL SOC

Superconducting phases of (NH3)(y)MxFeSe1-z Te-z have been synthesized by the intercalation of metal atoms (M: Li, Na, Ca) into FeSe and FeSe0.5Te0.5 using a low-temperature liquid NH3 technique. The superconducting transition temperature (T-c) is 31.5 K for Na-doped FeSe, and for Li-, Na-, and Ca-doped FeSe0.5Te0.5 it is 26, 22, and 17 K, respectively. The 31.5 K superconducting is the superconducting phase in ammoniated Na-doped FeSe. The T-c is lower than that (onset T-c = 46 K) of the superconducting phase reported previously. The reason why the T-c of this phase is lower is discussed based on the structure. The pressure dependences of T-c in the (NH3)(y)Na0.5FeSe and (NH3)(y)Na0.4FeSe0.5Te0.5 samples have been measured and a negative pressure dependence is observed; i.e., a decrease in lattice constant c leads to a decrease in Tc, consistent with the behavior of (NH3)(y)Cs0.4FeSe reported previously by our group. Furthermore, the magnetic behavior of (NH3)(y)Na0.4FeSe0.5Te0.5 has been fully investigated at different applied magnetic fields (H) to determine the critical magnetic This is a successful metal intercalation into FeSe1-z Te-z (z not equal 0) and an observation of superconductivity.

DOI： 10.1103/PhysRevB.89.144509

Charge Density Wave Transition in EuAl4 査読

Shingo Araki, Yoichi Ikeda, Tatsuo C. Kobayashi, Ai Nakamura, Yuichi Hiranaka, Masato Hedo, Takao Nakama, Yoshichika Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 83 ( 1 ) 015001-1-015001-2 2014年1月

Emergence of novel phase of solid oxygen in ultrahigh magnetic field 査読

T. C. Kobayashi, T. Nomura, Y. H. Matsuda, J. L. Her, S. Takeyama, A. Matsuo, K. Kindo

27TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT27), PTS 1-5 568 42018-1-42018-6 2014年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

Faraday discovered the magnetism of molecular oxygen in 1850, and since then, oxygen has attracted significant interests as a ubiquitous but exotic molecular magnet. In solid oxygen, the magnetic energy through the exchange interaction is comparable to the van der Waals cohesive energy, resulting in a strong spin-lattice correlation. We reported the discovery of a magnetic-field-induced phase transition of solid oxygen using ultrahigh magnetic fields up to 186 T. This is the first experiments demonstrating the phase control through the spin by applying a magnetic field. Magneto-optical absorption measurements of the a phase at low temperatures revealed that visible light absorption suddenly ceases and the background transparency dramatically improves above the critical field. The large hysteresis in these data indicates a first-order transition with a relaxation time on the order of microseconds. The results strongly suggest the reconstruction of the O-2 molecular geometry by the magnetic field, which causes that the antiferromagnetic phase collapses and the field-induced phase should have an isotropic crystal structure. Since all of the known phases of O-2 are induced in high pressure, the discovery of a field-induced phase is noteworthy in the long history of solid O-2 studies.

DOI： 10.1088/1742-6596/568/4/042018

Metamagnetic Transition of Itinerant Ferromagnet U3P4 under High Pressure 査読

Shingo Araki, Minami Hayashida, Naoto Nishiumi, Hiroki Manabe, Yoichi Ikeda, Tatsuo C. Kobayashi, Keizo Murata, Yoshihiko Inada, Piotr Wisniewski, Dai Aoki, Yoshichika Onuki, Etsuji Yamamoto, Yoshinori Haga

JPS Conference Proceedings 3 011081-1-011081-6 2014年

Pressure-Induced Magnetic Transition and Disappearance of Superconductivity in CeNiGe3 査読

Yoichi Ikeda, Takeshi Tomijima, Shingo Araki, Tatsuo C. Kobayashi, Keizo Murata

JPS Conference Proceedings 3 015044-1-015044-6 2014年

Valence crossover of Ce ions in CeCu2Si2 under high pressure –Pressure dependence of the unit cell volume and the NQR Frequency– 査読

T. C. Kobayashi, K. Fujiwara, K. Takeda, H. Harima, Y. Ikeda, T. Adachi, Y. Ohishi, C. Geibel, F. Steglich

J. Phys. Soc. Jpn. 82 ( 11 ) 114701-1-6 2013年11月

Superconductivity in (NH3)yCs0.4FeSe 査読

Lu Zheng, Masanari Izumi, Yusuke Sakai, Ritsuko Eguchi, Hidenori Goto, Yasuhiro Takabayashi, Takashi Kambe, Taiki Onji, Shingo Araki, Tatsuo C. Kobayashi, Jungeun Kim, Akihiko Fujiwara, Yoshihiro Kubozono

Physical Review B - Condensed Matter and Materials Physics 88 ( 9 ) 094521-094525 2013年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

Alkali-metal-intercalated FeSe materials, (NH3) yM0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)yCs 0.4FeSe shows a superconducting transition temperature (T c) as high as 31.2 K, which is higher by 3.8 K than the Tc of nonammoniated Cs0.4FeSe. The Tcs of (NH 3)yK0.4FeSe and (NH3) yRb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The Tc of (NH 3)yCs0.4FeSe shows a negative pressure dependence. A clear correlation between Tc and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.094521

Longitudinal magnetoresistance of Ce(Cu1-xNix)2Si2 査読

Yoichi Ikeda, Shingo Araki, Tatsuo C. Kobayashi

Journal of the Korean Physical Society 63 ( 3 ) 766 - 767 2013年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

The longitudinal magnetoresistance (LMR) of polycrystalline Ce(Cu1-xNix)2Si2 samples is investigated between T = 2 and 15 K up to H = 80 kOe. The application of magnetic field induces anomalous temperature dependence of the resistivity with the power index n &lt
2 for x = 0.12 and 0.14, in which ρ(T) obeys a T 2-law at H = 0 Oe. A sign-change of the LMR from positive (x &lt
0.03) to negative (x &gt
0.03) is observed at 2 K. The negative LMR at 80 kOe is maximized (∼ -4 % at T = 2 K) around x ∼ 0.10 and subsequently disappears at higher Ni concentrations. Disappearance of the positive LMR in lower x region and the negative LMR at higher Ni concentrations implies a collapse of a coherent Kondo lattice state, and a rapid enhancement of Kondo temperature, respectively. Anomalous quantum fluctuations are probably developed around x ∼ 0.10. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.766

Spin-dependent molecular orientation of O2–O2 dimer formed in the nanoporous coordination polymer 査読

A. Hori, T. C. Kobayashi, Y. Kubota, A. Matsuo, K. Kindo, J. Kim, K. Kato, M. Takata, H. Sakamoto, R. Matsuda, S. Kitagawa

J. Phys. Soc. Jpn. 82 ( 8 ) 084703-1-6 2013年8月

Pressure effects on rattling and superconductivity in the einstein solids 査読

Yoichi Ikeda, Yasuhiro Kawasaki, Takafumi Shinohara, Shingo Araki, Tatsuo C. Kobayashi, Atsushi Onosaka, Yoshihiko Okamoto, Jun-Ichi Yamaura, Zenji Hiroi

Journal of the Physical Society of Japan 82 ( 6 ) 063707-1-4 2013年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

Pressure effects on the rattling and superconductivity in the Einstein solids
AxV2Al20 (Ax = Ga0:2, Al0:3, and Y) are investigated by means of electrical resistivity measurements under high pressure. We observed bumps in resistivity at low temperatures only for Ga0:2 and Al0:3, which can be explained by scattering of conduction electrons by local phonons with Einstein temperatures of 8.5 and 22 K, respectively. The bumps gradually fade out with increasing pressure, and the temperature variations of resistivity for Ga0:2 and Al0:3 approach those of Y. This indicates that the low-energy local phonons in the Ga and Al compounds disappear at high pressures. We also observed T2 behavior with large A coefficients in the low-temperature limit for Ga and Al compounds, but not for Y. With increasing pressure, the A coefficient is largely suppressed, while H' c2 ≡ jdHc2=dTj Tc that also reflects the density of states at Fermi energy decreases more slowly. The T2 behavior in Ga and Al compounds probably originates from el-ph scatterings enhanced by rattling of Ga and Al atoms rather than el-el scatterings. An enhancement in the superconducting transition temperatures by the rattling is also demonstrated by comparing the pressure responses of T c between the three compounds. The enhancements of Tc and el-ph interaction λ is relatively small for these Einstein solids in contrast to those of the β-pyrochlore oxides. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.063707

Magneto-absorption in the α phase of solid oxygen at megagauss magnetic fields 査読

T. Nomura, Y. H. Matsuda, J. L. Her, S. Takeyama, A. Matsuo, K. Kindo, T. C. Kobayashi

Journal of Low Temperature Physics 170 ( 5-6 ) 372 - 376 2013年3月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Optical absorption spectra of solid oxygen α phase and liquid oxygen were measured in high magnetic fields over 100 T using a single turn coil method. The absorption originates from the bimolecular transition was observed. The spectra strongly reflect the local magnetic interaction between two oxygen molecules. The shape of the absorption spectrum of the α oxygen changed dramatically with increasing magnetic fields, even though the absorption intensity of liquid oxygen simply declined. This difference cannot be explained by only the local magnetic interaction, and we speculate that the field induced lattice distortion plays an important role in the solid oxygen α phase. © 2012 Springer Science+Business Media, LLC.

DOI： 10.1007/s10909-012-0699-z

インデンター型圧力セルとその応用

小手川恒, 小林達生

高圧力の科学と技術 = The Review of high pressure science and technology 22 ( 3 ) 214 - 221 2012年8月

記述言語：日本語出版者・発行元：The Japan Society of High Pressure Science and Technology

We review an indenter-type pressure cell, which possesses a maximum pressure of 5 GPa and a sample space of φ1.6×1.6 mm. This pressure cell is available not only for transport measurements but also for ac-susceptibility and NMR measurements. An advantage is the small size being able to change the direction of the pressure cell in the conventional superconducting magnet, which makes it possible to measure the anisotropy against magnetic field.<br>

DOI： 10.4131/jshpreview.22.214

その他リンク： https://jlc.jst.go.jp/DN/JALC/10008377707?from=CiNii

A Study of Ni-Substitution Effects on Heavy-Fermion CeCu2Si2 -Similarities between Ni Substitution and High-Pressure Effects 査読

Y. Ikeda, S. Araki, T. C. Kobayashi, Y. Shimizu, T. Yanagisawa, H. Amitsuka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( 8 ) 083701-1-083701-4 2012年6月

Iron-platinum-arsenide superconductors Ca10(PtnAs8)(Fe2−xPtxAs2)5 査読

Minoru,Nohara, Satomi Kakiya, Kazutaka Kudoa, Yoshihiro Oshiro, Shingo Araki, Tatsuo C. Kobayashi, Kenta Oku, Eiji Nishibori, Hi

Solid State Communications. 152 ( 8 ) 635 - 639 2012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：Elsevier

An overview of the crystal structures and physical properties of the recently discovered iron-platinum-arsenide superconductors, Ca-10(PtnAs8)(Fe2-xPtxAs2)(5) (n = 3 and 4), which have a superconducting transition temperature up to 38K, is provided. The crystal structure consists of superconducting Fe2As2 layers alternating with platinum-arsenic layers, PtnAs8. The upper critical field H-c2, hydrostatic pressure dependence of superconducting transition temperature T-c, and normal-state magnetic susceptibility are reported.

DOI： 10.1016/j.ssc.2011.12.034

Hall Effect in Single Crystal CeCu2Si2 under High Pressure 査読

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年

Cu-NQR of CeCu2Si2 under High Pressure 査読

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年

Interplay of superconductivity and Fermi-liquid transport in Rh-doped CaFe2As2 with lattice collapse transition 査読

M. Danura, K. Kudo, Y. Oshiro, S. Araki, T. C. Kobayashi, M. Nohara

J. Phys. Soc. Jpn. 80 ( 10 ) 103701-1-103701-4 2011年10月

Pressure-induced structural phase transitions in UIr 査読

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

Phys. Rev. B 84 (2011) 054524 84 ( 5 ) 054524-1-054524-5 2011年8月

Hall effect in CeCu2Si2 under pressure 査読

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

J. Phys. Soc. Jpn. 80 ( Suppl. A ) SA034-1-SA034-3 2011年7月

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

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( 2 ) 023715 2011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：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 査読

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

MICROPOROUS AND MESOPOROUS MATERIALS 129 ( 3 ) 296 - 303 2010年4月

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

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年4月

NQR study of pressure induced superconductivity in CeCu2Si2 査読

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年3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：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 査読

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

Journal of Physics: Conference Series 200 2010年1月

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 査読

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：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 査読

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：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 査読

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

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 ( 1 ) 69 - 76 2009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：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 査読

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年12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：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 査読

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：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 査読

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：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 査読

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：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 査読

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：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 査読

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：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 査読

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：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

Sb-NQR study of PrOs4Sb12 under high pressure 査読

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：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 査読

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年

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

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年

Appearance of the pressure-induced magnetic phase in alpha-manganese 査読

K. Takeda, A. Miyake, K. Shimizu, T. C. Kobayashi, K. Amaya

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

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 査読

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

COORDINATION CHEMISTRY REVIEWS 251 ( 21-24 ) 2510 - 2521 2007年11月

記述言語：英語出版者・発行元：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 査読

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

PHYSICAL REVIEW LETTERS 99 ( 15 ) 156408-1-156408-4 2007年10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：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 査読

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年5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：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 査読

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年3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：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 査読

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年3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

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 査読

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年3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

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 査読

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年3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

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 査読

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年3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

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 査読

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

REVIEW OF SCIENTIFIC INSTRUMENTS 78 ( 2 ) 23909-1-23909-5 2007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：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 査読

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年9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：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 査読

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年5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

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 査読

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年5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

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) 査読

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

PHYSICA B-CONDENSED MATTER 378-80 827 - 828 2006年5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

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 査読

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：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 査読

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：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 査読

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

PHYSICAL REVIEW LETTERS 96 ( 14 ) 2006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：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

Pressure-induced superconductivity emerging from antiferromagnetic phase in CeNiGe3 査読

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 4 ) 044713-1-6 2006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：PHYSICAL SOC JAPAN

The antiferromagnet CeNiGe3 exhibits superconductivity under pressure. The Neel temperature initially increases with increasing pressure up to 3GPa and then becomes zero at a critical pressure (P-C) that is located at approximately 7GPa. We found that superconductivity emerges from 1.7 GPa in the antiferromagnetic (AF) phase removed from P-C. The superconductivity is realized in a wide pressure region including P-C. The coefficient A in the resistivity and the upper critical field (H,2) significantly change against pressure. A feature of CeNiGe3 is that the moderate heavy fermion state in the AF phase induces superconductivity.

DOI： 10.1143/JPSJ.75.044713

Anisotropic residual resistivity under high pressure in UIr 査読

Akihiro Hori, Hiroyuki Hidaka, Hisashi Kotegawa, Tatsuo C. Kobayashi, Teruhiko Akazawa, Syugo Ikeda, Etsuji Yamamoto, Yoshinori Haga, Rikio Settai, Yoshichika Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 82 - 84 2006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：PHYSICAL SOC JAPAN

Anisotropic resistivity in UIr has been investigated under high pressure. A huge enhancement of residual resistivity was found under high pressure for the measuring current parallel to the [0 1 0] direction while any anomalies were not observed in the resistivity for [1 0 (1) over bar]. The residual resistivity for [0 1 0] reduced to the original value in the pressure range where superconductivity appears. This anomalous behavior indicates that the ground state in the high-rho(0) state is not simple ferromagnet and the application of pressure induces the first-order transition to slightly different electronic state.

DOI： 10.1143/JPSJS.75S.82

Metastable sorption state of a metal-organic porous material determined by in situ synchrotron powder diffraction 査読

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

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 45 ( 30 ) 4932 - 4936 2006年

Formation and characterization of crystalline molecular arrays of gas molecules in a 1-dimensional ultramicropore of a porous copper coordination polymer 査読

R Kitaura, R Matsuda, Y Kubota, S Kitagawa, M Takata, TC Kobayashi, M Suzuki

JOURNAL OF PHYSICAL CHEMISTRY B 109 ( 49 ) 23378 - 23385 2005年12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：AMER CHEMICAL SOC

Molecules and atoms confined in a nanospace may have properties distinctly different from those of the bulk fluid, owing to the formation of a specific molecular array characteristic of nanospace. In situ synchrotron powder X-ray diffraction measurements have been used to observe confined guest molecules such as N(2), O(2), Ar, and CH(4) in the well-regulated ultramicropore of a copper coordination polymer, 1 ([Cu(2),(pzdc)(2)pyz]: pzdc = 2,3-pyrazinedicarboxylate and pyz = pyrazine). The obtained crystal structures indicate that guest molecules are confined in a linear fashion to form crystal ine-like regular ordered arrays, in contrast to the situation in the gas and liquid state, even at temperatures above the boiling point, and the ordered arrays are characteristic of the kind of gas molecule and the geometrical and potential properties of the ultramicropore of 1.

DOI： 10.1021/jp054411j

Change of the Fermi surface across the critical pressure in CeIn3: The de Haas-van Alphen study under pressure 査読

R Settai, T Kubo, T Shiromoto, D Honda, H Shishido, K Sugiyama, Y Haga, TD Matsuda, K Betsuyaku, H Harima, TC Kobayashi, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 11 ) 3016 - 3026 2005年11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：PHYSICAL SOC JAPAN

We have studied a change of the Fermi surface in an antiferromagnet CeIn3 via the de Haas-van Alphen experiment under pressure up to 3 GPa. With increasing pressure P, the Neel temperature T-N = 10 K decreases and becomes zero at a critical pressure P-c similar or equal to 2.6 GPa. In the pressure region P > P,, we have observed a large main Fermi surface named a, which indicates that the electronic state of 4f electron in CeIn3 changes from localized to itinerant at P-c, as observed in the similar antiferromagnets CeRh2Si2 and CeRhIn5. The cyclotron effective mass m(c)(*) of this main Fermi surface is extremely enhanced around P-c: m(c)(*) similar or equal to 60m(0) at 2.7 GPa for the magnetic field along the (100) direction.

DOI： 10.1143/JPSJ.74.3016

Single crystal growth and fermi surface properties of an antiferromagnet UPdGa5 査読

S Ikeda, TD Matsuda, Y Haga, E Yamamoto, M Nakashima, S Kirita, TC Kobayashi, M Hedo, Y Uwatoko, H Yamagami, H Shishido, T Ueda, R Settai, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 8 ) 2277 - 2281 2005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：PHYSICAL SOC JAPAN

We have succeeded in growing a high-quality single crystal of an antiferromagnet UPdGa5 by the Ga-flux method with the off-stoichiometric composition of U : Pd : Ga = 1 : 2 : 7.3. The Neel temperature T-N = 30.5 K is found to increase with increasing the residual resistivity ratio (RRR) and becomes constant for a high-quality single crystal sample whose RRR is larger than 50. The electronic state has been investigated by the de Haas-van Alphen experiment, indicating the similar cylindrical Fermi surfaces as in an antiferromagnet UPtGa5. We have also studied the pressure effect by measuring the electrical resistivity. The Neel temperature decreases with increasing pressure and becomes zero at 3.1 GPa. The antiferromagnetic state is changed into the paramagnetic state above 3.1 GPa.

DOI： 10.1143/JPSJ.74.2277

Heavy fermion compound SmOs4Sb12 in vicinity of ferromagnetic critical point 査読

H Kotegawa, H Hidaka, Y Shimaoka, T Miki, TC Kobayashi, D Kikuchi, H Sugawara, H Sato

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 8 ) 2173 - 2176 2005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：PHYSICAL SOC JAPAN

We report nuclear quadrupole resonance (NQR) measurement at ambient pressure and resistivity measurement under high pressure in the new heavy fermion (HF) compound SmOs4Sb12. The NQR spectrum and the nuclear spin-lattice relaxation rate (1/T-1) clearly demonstrate the bulk nature of ferromagnetic ordering below T-C similar to 2 K. The temperature dependence of 1/T-1 exhibits the characteristic behaviors of a Kondo lattice. The application of pressure decreases Kondo temperature and stabilizes the magnetic ordering, which is the same tendency as that found in some Yb-based compounds. The obtained phase diagram indicates SmOs4Sb12 to be in the vicinity of its ferromagnetic critical point.

DOI： 10.1143/JPSJ.74.2173

Highly controlled acetylene accommodation in a metal-organic microporous material 査読

R Matsuda, R Kitaura, S Kitagawa, Y Kubota, RV Belosludov, TC Kobayashi, H Sakamoto, T Chiba, M Takata, Y Kawazoe, Y Mita

NATURE 436 ( 7048 ) 238 - 241 2005年7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：NATURE PUBLISHING GROUP

Metal - organic microporous materials(1-4) (MOMs) have attracted wide scientific attention owing to their unusual structure and properties, as well as commercial interest due to their potential applications in storage(5-9), separation(10,11) and heterogeneous catalysis(12,13). One of the advantages of MOMs compared to other microporous materials, such as activated carbons, is their ability to exhibit a variety of pore surface properties such as hydrophilicity and chirality, as a result of the controlled incorporation of organic functional groups into the pore walls(11,13-15). This capability means that the pore surfaces of MOMs could be designed to adsorb specific molecules; but few design strategies for the adsorption of small molecules have been established so far. Here we report high levels of selective sorption of acetylene molecules as compared to a very similar molecule, carbon dioxide, onto the functionalized surface of a MOM. The acetylene molecules are held at a periodic distance from one another by hydrogen bonding between two non-coordinated oxygen atoms in the nanoscale pore wall of the MOM and the two hydrogen atoms of the acetylene molecule. This permits the stable storage of acetylene at a density 200 times the safe compression limit of free acetylene at room temperature.

DOI： 10.1038/nature03852

De Haas-van Alphen effect in CeIn3 under pressure 査読

Rikio Settai, Tetsuo Kubo, Hiroaki Shishido, Tatsuo C. Kobayashi, Yoshichika Onuki

Physica B: Condensed Matter 359-361 317 - 319 2005年4月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

We have investigated a change of the electronic state in CeIn3 via de Haas-van Alphen (dHvA) experiments under pressure up to 2.72 GPa for the magnetic field along 〈110〉. A main Fermi surface with the dHvA frequency F=9.4×107 Oe and a large cyclotron mass mc*=53m0 was observed at 2.72 GPa in the vicinity of the critical pressure where the Néel temperature is suppressed to zero. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.119

Magnetization study of heavy Fermion superconductor URu2Si2 under high pressures 査読

K Tenya, Kawasaki, I, K Tameyasu, S Yasuda, M Yokoyama, H Amitsuka, N Tateiwa, TC Kobayashi

PHYSICA B-CONDENSED MATTER 359 1135 - 1137 2005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：ELSEVIER SCIENCE BV

Magnetization measurements of URu2Si2 have been performed under hydrostatic pressures. The superconducting transition temperature decreases linearly with pressure up to 1.1 GPa and disappears above 1.5 GPa. The hysteretic magnetization shows characteristic behaviors at high pressures, suggesting that the pinning properties are changed due to the switch of the normal state to the antiferromagnetic state. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.325

Metal-insulator transition under high pressure in PrFe4P12 査読

H Hidaka, Ando, I, H Kotegawa, TC Kobayashi, H Harima, M Kobayashi, H Sugawara, H Sato

PHYSICA B-CONDENSED MATTER 359 886 - 888 2005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：ELSEVIER SCIENCE BV

We have studied the electrical resistivity in a skutterudite compound PrFe4P12 under high pressure. An antiferroquadrupolar ordering temperature T-Q decreases monotonously with increasing pressure up to 2.4 GPa. Above 2.4 GPa, the metal-insulator (M-I) transition appears. By applying magnetic field, this M-I transition is suppressed easily and heavy-fermion state is realized. The observed Kondo effect and the field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions of the f electrons of Pr3+ survive even in the insulator phase. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.334

High-pressure effect on the electrical resistivity in CeNiGe3 and CeNi2Al5 査読

M Nakashima, K Tabata, A Thamizhavel, TC Kobayashi, M Hedo, Y Uwatoko, K Shimizu, R Settai, Y Onuki

PHYSICA B-CONDENSED MATTER 359 266 - 268 2005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：ELSEVIER SCIENCE BV

We have measured the electrical resistivity of antiferromagnetic Kondo compounds CeNiGe3 and CeNi2Al5 under pressure. In CeNiGe3, Neel temperature T-N initially increases with increasing pressure P up to 3 GPa, then decreases rather steeply with further increasing pressure, and becomes zero at a critical pressure P-c similar or equal to 5.5 GPa. The A and rho(0) values of the resistivity rho = rho(0) + AT(2) in the Fermi liquid relation become maximum around P-c. Superconductivity is found below 0.48 K in a wide pressure region from 4 to 10 GPa. In CeNi2Al5, the similar pressure dependence of TN is found, has a maximum at 3.9 GPa, and becomes zero around 6 GPa. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/i.physb.2005.01.066

Pressure-induced charge ordering of LiV2O4 査読

K Takeda, H Hidaka, H Kotegawa, TC Kobayashi, K Shimizu, H Harima, K Fujiwara, K Miyoshi, J Takeuchi, Y Ohishi, T Adachi, M Takata, E Nishibori, M Sakata, T Watanuki, O Shimomura

PHYSICA B-CONDENSED MATTER 359 1312 - 1314 2005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：ELSEVIER SCIENCE BV

The powder X-ray diffraction experiments of LiV2O4 have been performed at low temperature and high pressure using synchrotron radiation. In the isothermal experiment at 10 K, the cubic-rhombohedral phase transition corresponding to the metal-insulator transition is found at around 13 GPa. This transition seems to be due to charge ordering of V ions on the analogy of the metal-insulator transition in AlV2O4. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.390

Pressure-induced superconductivity in UIr without inversion symmetry 査読

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

PHYSICA B-CONDENSED MATTER 359 1138 - 1140 2005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：ELSEVIER SCIENCE BV

Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure-temperature phase diagram has been investigated by means of electrical resistivity and magnetization. The phase diagram consists of two ferromagnetic phases. The ferromagnetic phase FM1 with T-Cl similar to 46 K at ambient pressure disappears around 1.7 GPa. With further increase of pressure, the phase (FM2) with small ferromagnetic moment appears in the pressure range of P-Cl < P < 2.6 GPa. The superconducting phase exists near the disappearance point of the FM2 phase, indicating that the superconductivity is associated with the ferromagnetic critical fluctuation around P-C2. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.335

Pressure-induced metal-insulator transition in the filled skutterudite PrFe4P12 査読

H Hidaka, Ando, I, H Kotegawa, TC Kobayashi, H Harima, M Kobayashi, H Sugawara, H Sato

PHYSICAL REVIEW B 71 ( 7 ) 2005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：AMER PHYSICAL SOC

We have studied the electrical resistivity of the filled skutterudite compound PrFe4P12 under high pressure. The antiferroquadrupolar ordering temperature T-Q decreases monotonically with increasing pressure up to 2.4 GPa. Above 2.4 GPa, we have found that a metal-insulator (M-I) transition appears. The insulating state is easily suppressed by a magnetic field. The observed Kondo effect and a field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions survive in the insulating region. The quadrupolar interactions might play an essential role in the M-I transition. PrFe4P12 is an unusual compound in that it shows a pressure-induced transition from a metal to an insulator.

DOI： 10.1103/PhysRevB.71.073102

Pressure-induced metal-insulator transition in the filled skutterudite PrFe <inf>4</inf>P <inf>12</inf> 査読

Hiroyuki Hidaka, Ikuma Ando, Hisashi Kotegawa, Tatsuo C. Kobayashi, Hisatomo Harima, Miki Kobayashi, Hitoshi Sugawara, Hideyuki Sato

Physical Review B - Condensed Matter and Materials Physics 71 ( 7 ) 2005年2月

掲載種別：研究論文（学術雑誌）

We have studied the electrical resistivity of the filled skutterudite compound PrFe 4P 12 under high pressure. The antiferroquadrupolar ordering temperature T Q decreases monotonically with increasing pressure up to 2.4 GPa. Above 2.4 GPa, we have found that a metal-insulator (M-I) transition appears. The insulating state is easily suppressed by a magnetic field. The observed Kondo effect and a field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions survive in the insulating region. The quadrupolar interactions might play an essential role in the M-I transition. PrFe 4P 12 is an unusual compound in that it shows a pressure-induced transition from a metal to an insulator. ©2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.073102

Direct observation of hydrogen molecules adsorbed in a microporous coordination polymer 査読

Y. Kubota, M. Takata, R. Matsuda, R. Kitaura, S. Kitagawa, K. Kato, M. Sakata, T. C. Kobayashi

Angew. Chem. Int. Ed. 2005年

Magnetic properties of molecular oxygen adsorbed in micro-porous metal-organic solids 査読

TC Kobayashi, A Matsuo, M Suzuki, K Kindo, R Kitaura, R Matsuda, S Kitagawa

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT ( 159 ) 271 - 279 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE

The magnetic properties of O-2 adsorbed in nanochannels of porous metal-organic solids CPL-1 and CPL-p1 have been investigated by means of high-field magnetization process measurement. The contribution from adsorbed 02 shows the metamagnetic-like behavior in both compounds. We propose "the field-induced rearrangement mechanism" as the explanation for the metamagnetic-like behavior. It is known for the O-2-O-2 dimer that the magnetic interaction depends strongly on the intermolecular distance and the orientation of molecular axes. It is considered naturally that the stable arrangement with saturated magnetic moment in the sufficient high field is different from the H-structure which is stable at zero field.

DOI： 10.1143/PTPS.159.271

Guest shape-responsive fitting of porous coordination polymer with shrinkable framework 査読

R Matsuda, R Kitaura, S Kitagawa, Y Kubota, TC Kobayashi, S Horike, M Takata

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 126 ( 43 ) 14063 - 14070 2004年11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：AMER CHEMICAL SOC

In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers {[Cu-2-(pzdc)(2)(bpy)](.)G} have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H2O for CPL-2 superset of H2O, G = benzene for CPL-2 superset of benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset of benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds.

DOI： 10.1021/ja046925m

Pressure-induced superconductivity in UIr 査読

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 11 ) 3129 - 3134 2004年11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：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 and magnetization measurements under high pressure. The phase diagram consists of two magnetic phases, the Ising-like ferromagnetic phase (FM1) at low pressures and another magnetic phase (FM2) with the small ferromagnetic component along the [101] direction at high pressures. Superconductivity is observed in the narrow pressure range near the disappearance point of the FM2 phase, where the temperature dependence of resistivity follows the non-Fermi liquid form of T-1.6. From these experimental facts, the superconductivity is considered to be associated with the critical fluctuation with the disappearance of FM2 phase.

DOI： 10.1143/JPSJ.73.3129

Magnetization and Magnetoresistance measurements up to 60 T at 70 mK 査読

Y. Narumi, N. Takamoto, K. Kindo, T. C. Kobayashi, N. Shimizu, F. Iga, S. Hiura, T. Takabatake, M. Vendaguer

World Scientific Publishing Co. Pre. Ltd. 2004年11月

Rational design and crystal structure determination of a 3-D metal-organic jungle-gym-like open framework 査読

R Kitaura, F Iwahori, R Matsuda, S Kitagawa, Y Kubota, M Takata, TC Kobayashi

INORGANIC CHEMISTRY 43 ( 21 ) 6522 - 6524 2004年10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：AMER CHEMICAL SOC

A new three-dimensional (3-D) jungle-gym-like open metal-organic framework has been synthesized from a two-dimensional (2-D) layer compound using a heterogeneous pillar insertion reaction. Both the starting 2-D layer and the resulting 3-D open compounds have been characterized using X-ray crystallography.

DOI： 10.1021/ic049005d

Heat-capacity anomalies at T-sc and T-* in the ferromagnetic superconductor UGe2 査読

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

PHYSICAL REVIEW B 69 ( 18 ) 2004年5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：AMER PHYSICAL SOC

The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe2. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature T-* where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at T-* at least under high pressure slightly below P-c(*) where T-* becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of C/T is observed in a narrow pressure region (DeltaPsimilar to0.1 GPa) around P-c(*) contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point P-c(*) for the appearance of the superconductivity.

DOI： 10.1103/PhysRevB.69.180513

Heat-capacity anomalies at Tsc and T* in the ferromagnetic superconductor UGe2 査読

N. Tateiwa, T. C. Kobayashi, K. Amaya, Y. Haga, R. Settai, Y. Onuki

Physical Review B - Condensed Matter and Materials Physics 69 ( 18 ) 1 - 180513 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe2. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature T* where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at T* at least under high pressure slightly below P*c where T* becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of C/T is observed in a narrow pressure region (ΔP∼0.1 GPa) around P* contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point P*c for the appearance of the superconductivity.

DOI： 10.1103/PhysRevB.69.180513

A change of the Fermi surface in CeIn3 under pressure 査読

R Settai, T Kubo, H Shishido, TC Kobayashi, Y Onuki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 223 - 224 2004年5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

We have investigated a change of the electronic state in CeIn3 via de Haas-van Alphen (dHvA) experiments under pressure up to 2.7 GPa. The shape of a spherical Fermi surface with humps along <111> changes slightly at 2.5 GPa. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.200

Magnetism of uranium dioxide UO2 under high pressure 査読

H. Sakai, H. Kato, Y. Tokunaga, S. Kambe, R. E. Walstedt, A. Nakamura, N. Tateiwa, C. Kobayashi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 E413 - E414 2004年5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

The DC magnetization of insulating UO2 under high pressure up to similar to 1 GPa has been measured using a piston-cylinder cell. Pressure-induced weak ferromagnetism was found to appear at low pressure (similar to 0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.307

Magnetism of a one-dimensional array of oxygen in a micro-porous metal-organic solid 査読

A. Matsuo, T. C. Kobayashi, M. Suzuki, K. Kindo, R. Kitaura, R. Matsuda, H. -C. Chang, S. Kitagawa

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 E643 - E645 2004年5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

The magnetic properties of molecular oxygen adsorbed in the micro-porous metal-organic solids have been investigated. Adsorbed O-2 molecules form a ladder structure in the nanochannels of CPL-1. The temperature dependence of susceptibility and the high-field magnetization process indicate the nonmagnetic ground state of the adsorbed O-2 at low temperatures. (C) 2003 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.327

Evidence for the pressure induced magnetic ordering in YbInCu4 査読

Takeshi Mito, Takehide Koyama, Shinji Wada, Takaki Muramatsu, Tatsuo C. Kobayashi, John L. Sarrao

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 E47 - E48 2004年5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

We have carried out electrical resistivity rho and AC-susceptibility chi(AC) measurements on YbInCu4 under pressure. For pressures above 2.49 GPa, the first-order valence transition is completely suppressed and a clear peak appears in chi(AC) with a small kink in rho at T-M = 2.4 K. The chi(AC) peak is easily diminished by applying low magnetic fields and disappears above similar to 500 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 phase of YbInCu4 is most probably a ferromagnetically ordered state. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.146

Recent advances in the magnetism and superconductivity of heavy fermion systems 査読

Y Onuki, R Settai, K Sugiyama, T Takeuchi, TC Kobayashi, Y Haga, E Yamamoto

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 4 ) 769 - 787 2004年4月

記述言語：英語出版者・発行元：PHYSICAL SOC JAPAN

We present recent advances in the magnetism and superconductivity of rare earth and uranium compounds. Heavy fermions are formed on the basis of the competition between the RKKY interaction and the Kondo effect in these compounds. The application of pressure to these compounds is useful to control the electronic states in the antiferromagnets CeRh2Si2 and CeRhIn5, and the ferromagnet UGe2. The quadrupole interaction or the quadrupole Kondo effect is found to be responsible for heavy fermions in PrFe4P12. A rich variety of superconducting properties are demonstrated: superconductivity of CeCoIn5 and CeRhIn5 in the vicinity of a quantum critical point, coexistence of ferromagnetism and superconductivity in UGe2, and superconductivity based on the quadrupole fluctuations in PrOs4Sb12, together with the relation between the superconducting transition temperature and the quasi-two dimensionality of the electronic states.

DOI： 10.1143/JPSJ.73.769

Observation of a transient magnetization plateau in a quantum antiferromagnet on the Kagome lattice 査読

Y Narumi, K Katsumata, Z Honda, JC Domenge, P Sindzingre, C Lhuillier, Y Shimaoka, TC Kobayashi, K Kindo

EUROPHYSICS LETTERS 65 ( 5 ) 705 - 711 2004年3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：E D P SCIENCES

The magnetization process of an S = 1/2 antiferromagnet on the Kagome lattice, [Cu-3(titmb)(2)(OCOCH3)(6)] . H2O{titmb = 1, 3, 5-tris(imidazol-1-ylmethyl)-2.4.6 trimethyl-benzene}, has been measured at very low temperature's in both pulsed and steady fields. We have found a new dynamical behavior in the magnetization process. A plateau at one third of the saturation magnetization M-s appears in the pulsed-field experiments for intermediate sweep rates of the magnetic field and disappears in the steady-field experiment's. A theoretical analysis using exact diagonalization yields J(1) = 19+/-2 K and J(2) = 6+/-2 K. for the nearest-neighbor and second-nearest-neighbor interactions. respectively. This set of exchange parameters explains the very low saturation field and the absence of the plateau in the thermodynamic equilibrium as well as the two-peak feature in the magnetic heat. capacity observed by Honda et. al. (Z. Honda et al., J. Phys. Condens. Matter. 14 (2002) L625). Supported by numerical results we argue that a dynamical order by disorder phenomenon could explain the transient appearance of the M-s/3 plateau in pulsed-field experiments.

DOI： 10.1209/epl/i2003-10164-5

LiNMR in LiV2O4 under high pressure 査読

K Fujiwara, K Miyoshi, J Takeuchi, Y Shimaoka, T Kobayashi

JOURNAL OF PHYSICS-CONDENSED MATTER 16 ( 11 ) S615 - S619 2004年3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：IOP PUBLISHING LTD

The Knight shift K and the nuclear spin-lattice relaxation time T-1 of Li-7 have been measured under high pressure up to 4.74 GPa. 1/T1T becomes larger on applying higher pressure below 10 K and does not obey the T1T = constant relation down to 1 K. Meanwhile, K is independent of pressure above 2 GPa, indicating that the uniform component of the susceptibility does not change under high pressure. These results indicate that some antiferromagnetic fluctuations with wavevector q not equal 0 dominate the relaxation rate in LiV2O4 near the boundary of the pressure induced insulating phase. It is noted that the pressure dependence of T-1 for LiV2O4 is opposite to that of typical Ce HF compounds, such as CeCu5.9Au0.1 and CeCu2Si2. At the highest pressure of 4.74 GPa, we found that 1/T-1 obeys a power law dependence of T-2/3 over the wide T range between 60 mK and 10 K. The spin dynamics under high pressure will be discussed.

DOI： 10.1088/0953-8984/16/11/007

Electrical, Thermal and Magnetic Properties of CeNiIn4 査読

Hiroaki Shishido, Noriko Nakamura, Taiki Ueda, Rihito Asai, Andrei Galatanu, Etsuji Yamamoto, Yoshinori Haga, Tetsuya Takeuchi, Yasuo Narumi, Tatsuo C Kobayashi, Koichi Kindo, Kiyohiro Sugiyama, Takahiro Namiki, Yuji Aoki, Hideyuki Sato, Yoshichika Ōnuki

Journal of the Physical Society of Japan 73 ( 3 ) 664 - 668 2004年3月

Pressure-induced superconductivity in ferromagnetic UIr without inversion symmetry 査読

T Akazawa, H Hidaka, T Fujiwara, TC Kobayashi, E Yamamoto, Y Haga, R Settai, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 16 ( 4 ) L29 - L32 2004年2月

記述言語：英語出版者・発行元：IOP PUBLISHING LTD

We report the discovery of pressure-induced superconductivity in ferromagnetic UIr, which lacks inversion symmetry in the crystal structure. The Curie temperature T-CI = 46 K at ambient pressure decreases with increasing pressure, reaching a value of 11 K at 1.5 GPa. It presumably decreases further up to about P-cl = 1.7 GPa. The ferromagnetic region named 'Fl' exists up to P-cl. A second magnetic phase named 'F2' with a low ferromagnetic moment appears in the pressure range frorn 1.9 to 2.4 GPa. In the 'F2' phase, the magnetic transition temperature T-C2 decreases with pressure, from 18 K at 1.9 GPa to approximately zero at P-C2 = 2.6-2.7 GPa. In this critical pressure region, superconductivity appears below T-sc = 0.14 K.

DOI： 10.1088/0953-8984/16/4/L02

Dissimilarity between metallic-like transport in the dielectric spin density wave and field-induced spin density wave states in (TMTSF) <inf>2</inf>PF<inf>6</inf> 査読

A. V. Kornilov, V. M. Pudalov, Y. Kitaoka, K. Ishida, T. Mito, N. Tateiwa, T. C. Kobayashi, J. S. Qualls

JETP Letters 80 ( 11 ) 707 - 710 2004年

掲載種別：研究論文（学術雑誌）

We report similarities and differences of the transport features in the spin density wave (SDW) and in the field-induced SDW (FISDW) phases of the quasi-one-dimensional compound (TMTSF)"2PF"6. As temperature decreases below ≈2 K, the resistance in both phases exhibits a maximum and a subsequent strong drop. However, the characteristic temperature of the R(T) maximum and its scaling behavior in different magnetic fields B are evidence that the nonmonotonic R(T) dependences have different origin in SDW and FISDW regions of the phase diagram. We also found that the borderline T"0(B, P) which divides the FISDW region of the P-B-T phase diagram into the hysteresis and nonhysteresis domains terminates in the N = 1 subphase; the borderline thus has no extension to the SDW N = 0 phase. © 2004 MAIK "Nauka/Interperiodica".

DOI： 10.1134/1.1862799

High-pressure effect on the electronic state in CeNiGe3: Pressure-induced superconductivity 査読

M. Nakashima, K. Tabata, A. Thamizhavel, T. C. Kobayashi, M. Hedo, Y. Uwatoko, K. Shimizu, R. Settai, Y. Onuki

J. Phys.: Condens. Matter 16 ( 20 ) 2004年

Low temperature magnetic properties of CeTBi2 (T : Ni, Cu and Ag) single crystals 査読

A Thamizhavel, A Galatanu, E Yamamoto, T Okubo, M Yamada, K Tabata, TC Kobayashi, N Nakamura, K Sugiyama, K Kindo, T Takeuchi, R Settai, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 10 ) 2632 - 2639 2003年10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：PHYSICAL SOC JAPAN

A series of the ternary compounds CeTBi2 (T: Ni, Cu and Ag) have been grown in the single crystalline form by means of the flux method. These compounds crystallize in the tetragonal crystal structure. Measurements of the electrical resistivity, magnetic susceptibility, magnetization, low temperature specific heat and de Haas-van Alphen effect are reported. These compounds order antiferromagnetically with an easy-axis of magnetization along the [001] direction(c-axis). The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the quasi-two dimensional crystal structure.

DOI： 10.1143/JPSJ.72.2632

Magnetic properties and a change of the electrical resistivity under pressure in CePtGe2 査読

S Kirita, A Thamizhavel, T Takeuchi, K Tabata, TC Kobayashi, A Galatanu, E Yamamoto, R Settai, S Ramakrishnan, Y Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 9 ) 2338 - 2343 2003年9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：PHYSICAL SOC JAPAN

We have succeeded in growing a single crystal of CePtGe2 with the orthorhombic crystal structure by the Bi-flux method. In order to investigate the anisotropic properties, the magnetic susceptibility, magnetization and electrical resistivity measurements have been performed along the principal axes. From these measurements, it is found that CePtGe2 orders ferromagnetically below T-C = 5.1 K, and the magnetic easy-axis corresponds to the a-axis. The anisotropic properties have been analyzed on the basis of the crystalline electric field model. We have also studied the pressure effect on the ferromagnetic ordering, and T-C is found to increase with increasing pressure. However, T-C smears out around 3.5 GPa and a new phase appears at higher pressures, where the transition temperature of the new phase also increases with increasing pressure.

DOI： 10.1143/JPSJ.72.2338

Pressure-induced weak ferromagnetism in uranium dioxide, UO2 査読

H Sakai, H Kato, Y Tokunaga, S Kambe, RE Walstedt, A Nakamura, N Tateiwa, TC Kobayashi

JOURNAL OF PHYSICS-CONDENSED MATTER 15 ( 28 ) S2035 - S2037 2003年7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：IOP PUBLISHING LTD

The do magnetization of insulating UO2 under high pressure up to similar to 1 GPa has been measured using a piston-cylinder cell. Pressure-induced weak ferromagnetism appeared at low pressure (similar to0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries.

DOI： 10.1088/0953-8984/15/28/321

An anomalously huge resistivity peak under pressure in CeRhGe 査読

R Asai, A Thamizhavel, H Shishido, T Ueda, Y Inada, R Settai, C Kobayashi, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 15 ( 29 ) L463 - L468 2003年7月

記述言語：英語出版者・発行元：IOP PUBLISHING LTD

We have measured the electrical resistivity under pressure up to 2 GPa for an antiferromagnet, CeRhGe. The resistivity at ambient pressure decreases monotonically below a Neel temperature T-N = 10 K. With increasing pressure P, the resistivity has a peak around 10 K, which is anomalously enhanced up to 1.2 GPa. With further increasing pressure, the resistivity peak is diminished; the Neel temperature becomes zero at a critical pressure P-c = 9 GPa. The A-value of the resistivity rho in the Fermi liquid relation rho = rho(0) +AT(2) is also found to increase with increasing pressure and has a maximum at Pc which corresponds to the value for the heavy-fermion superconductor CeCu2Si2.

DOI： 10.1088/0953-8984/15/29/102

Magnetic properties of a S = 1/2 zigzag spin chain compound (N2H5)CuCl3 査読

N Maeshima, M Hagiwara, Y Narumi, K Kindo, TC Kobayashi, K Okunishi

JOURNAL OF PHYSICS-CONDENSED MATTER 15 ( 21 ) 3607 - 3618 2003年6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：IOP PUBLISHING LTD

We present a theoretical and experimental study of a quasi-one-dimensional zigzag antiferromagnet (N2H5)CuCl3, which can be viewed as weakly coupled Heisenberg chains with a frustrated interaction. We first discuss generic features of the magnetic properties of the zigzag spin chain between the nearly single chain case and the nearly double chain case, on the basis of the finite temperature density-matrix renormalization group (DMRG) calculations. We next show the experimental results for the magnetic susceptibility and the high-field magnetization of a single crystal of (N2H5)CuCl3 above the Neel temperature T-N = 1.55 K. By comparing the experimental data with the DMRG results carefully, we finally obtain the ratio of the nearest and next-nearest exchange couplings as J(1)/J(2) = 0.25 with J(2)/k(B) = 16.3 K. We also investigate the three-dimensional (3D) coupling J' effect by using mean-field theory combined with the DMRG calculations. The estimated value J' similar to 0.04J(2) supports the one-dimensionality of (N2H5)CuCl3 above T-N.

DOI： 10.1088/0953-8984/15/21/309

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

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年6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

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 査読

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

PHYSICAL REVIEW B 67 ( 22 ) 2003年6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：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 査読

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

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 527 - 528 2003年5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

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 査読

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

PHYSICA B-CONDENSED MATTER 329 1209 - 1210 2003年5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

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 ferromagnetic superconductor UGe2 査読

N. Tateiwa, T. C. Kobayashi, K. Amaya, Y. Haga, R. Settai, Y. Onuki

Acta Physica Polonica B 34 ( 2 ) 515 - 518 2003年2月

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

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：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 査読

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：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 査読

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

Physica C 2003年

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

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年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読

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

PHYSICAL REVIEW B 66 ( 21 ) 2002年12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：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 査読

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年12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：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 査読

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

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 44 ) 10779 - 10782 2002年11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：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 査読

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年6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：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 査読

S Araki, M Nakashima, R Settai, TC Kobayashi, Y Onuki

JOURNAL OF PHYSICS-CONDENSED MATTER 14 ( 21 ) L377 - L383 2002年6月

記述言語：英語出版者・発行元：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 査読

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年4月

記述言語：英語出版者・発行元：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 査読

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

PHYSICA B-CONDENSED MATTER 312 109 - 111 2002年3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

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 査読

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年3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

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 査読

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

PHYSICA B-CONDENSED MATTER 312 913 - 915 2002年3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

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 査読

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：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 査読

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：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

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

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年1月

記述言語：英語出版者・発行元：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) 査読

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：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 査読

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：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 査読

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

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

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

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

その他リンク： 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 査読

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年

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読

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

J. Phys. Soc. Jpn. 2002年

Thermal properties of a ferromagnetic superconductor UGe2 査読

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

Journal of Nuclear Science and Technology 39 195 - 198 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読

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年

記述言語：英語掲載種別：研究論文（学術雑誌）

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)] 査読

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年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 査読

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年12月

Fermi surface instability in CeRh2Si2 under pressure 査読

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

Physical Review B - Condensed Matter and Materials Physics 64 ( 22 ) 2244171 - 2244177 2001年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読

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

PHYSICAL REVIEW B 64 ( 22 ) 2001年12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：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 査読

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年11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：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 査読

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年10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：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) 査読

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

JOURNAL OF PHYSICS-CONDENSED MATTER 13 ( 29 ) 6443 - 6443 2001年7月

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

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 226 414 - 416 2001年5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

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 査読

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 226 423 - 424 2001年5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

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 査読

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年3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：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 査読

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

PHYSICA B 294 271 - 275 2001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 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 査読

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

JOURNAL OF PHYSICS-CONDENSED MATTER 13 ( 1 ) L17 - L23 2001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：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

High-quality single-crystal growth and a change of the electronic states under pressure in CeRh2Si2 査読

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

Journal of Magnetism and Magnetic Materials 226-230 ( I ) 80 - 82 2001年

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

We succeeded in growing a high-quality single crystal of CeRh2Si2 with a residual resistivity ratio of 110. Under a pressure of 1.1 GPa, superconductivity is found below Tc = 0.38 K, where a Néel temperature of TN = 36K is suppressed down to almost zero. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00785-X

Neutron scattering studies in the linear-chain Haldane materials, NDMAZ and NDMAP 査読

Y Koike, N Metoki, Y Morii, T Kobayashi, T Ishii, M Yamashita

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 ( 12 ) 4034 - 4042 2000年12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：PHYSICAL SOC JAPAN

Neutron scattering experiments were carried out in order to investigate the field-induced. antiferromagnetic long-range order and spin dynamics for the new Haldane compounds Ni(C5H14N2)(2)N-3 (ClO4) (NDMAZ) and Ni(C5H14N2)(2)N-3 (PF6) (NDMAP). We observed the energy gaps corresponding to the excited triplet, Delta (chi) = 1.61 meV, Delta (gamma) = 1.76 meV, Delta (z) = 3.2 meV for NDMAZ and Delta (chi), = 0.48 meV, Delta (gamma), = 0.64 meV for NDMAP. The dispersion in NDMAZ was well explained by the theoretical curve with the intra-chain interaction J = 50 K. The field dependence of the gap energy below critical field (H-c), was observed for NDMAZ and NDMAP as applying the field perpendicular to the chain direction. The field dependence of the excitation levels in NDMAZ was well explained by the fermionic field-theory treatment of the one-dimensional Heisenberg antiferromagnetic Hamiltonian with these gap energies and g-value, 2.3. In NDMAP, we found that the excitation peaks at Q = (0 0 0.5) became unobservably weak above H-c. This result would indicate a level crossing between the ground and the excited level at H-c and the change of the ground state above H-c. No trace of the magnetic Bragg peak due to the field induced ordering could be observed in the present study with our non-deuterated single crystal sample.

DOI： 10.1143/JPSJ.69.4034

Specific heat and effect of pressure on the electrical resistivity of CePtGa single crystal 査読

Y Uwatoko, M Kosaka, M Shirakawa, G Oomi, N Mori, T Kobayashi, H Tatewaki, K Shimizu, K Amaya

PHYSICA B 284 1321 - 1322 2000年7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

Specific heat and effect of pressure on the electrical resistivity of CePtGa single crystal have been measured upto 30 kbar. A sharp peak in the ratio of specific heat to temperature and in electrical resistivity is observed at 33 and 3.5 K, respectively, which is ascribed to an antiferromagnetic transition. The results reveal that T-N decreases linearly with increasing pressure upto 30 kbar. (C) 2000 Elsevier Science B.V. All rights reserved.

Pressure dependence of quadrupole ordering temperature T-Q in CeB6 査読

TC Kobayashi, K Hashimoto, S Eda, K Shimizu, K Amaya, Y Onuki

PHYSICA B 281 553 - 554 2000年6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

Pressure dependence of electrical resistance in CeB6 is investigated up to 13 GPa. A maximum in temperature dependence of the resistance shifts to higher temperature by the application of pressure. The quadrupole ordering temperature T-Q shows no obvious pressure dependence at zero field, while the field dependence of T-Q is enhanced slightly under high pressure. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)00947-3

Metamagnetic transition of CeRh2Si2 under high fields and high pressures at various temperatures 査読

T Hamamoto, K Kindo, TC Kobayashi, Y Uwatoko, S Araki, R Settai, Y Onuki

PHYSICA B 281 64 - 65 2000年6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

High-field magnetization measurements in a heavy fermion antiferromagnet CeRh2Si2 were performed under high pressures at various temperatures to study the nature of the metamagnetism. Metamagnetic transitions were observed not only in the antiferromagnetic state but also in the paramagnetic stale at various pressures, The metamagnetism in CeRh2Si2 does not originate from the rearrangement of antiferromagnetic moments but from the recovery of the local moment from the Kondo singlet state by applying high magnetic fields. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Pressure-dependence of superconducting behavior in CeRh2Si2 査読

TC Kobayashi, T Muramatsu, M Takimoto, K Hanazono, K Shimizu, K Amaya, S Araki, R Settai, Y Onuki

PHYSICA B 281 7 - 8 2000年6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

Electrical resistance has been investigated in a high-quality polycrystal of CeRh2Si2 under high pressures of up to 5.4 GPa. We found a resistance drop corresponding to superconductivity in the pressure range from 0.7 to 2.9 GPa. The relative decrease of the resistance shows a maximum in the vicinity of a critical pressure Pc. An onset temperature of superconductivity is about 0.6 K. (C) 2000 Elsevier Science B.V. All rights reserved.

Electrical studies in DAC 査読

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

Sci. & Tech. of High Pressure ( 5 ) 218 - 222 2000年

Electrical resistance measurement in hydrostatic pressure up to 10 GPa using a diamond anvil cell 査読

K. Shimizu, T. C. Kobayashi, T. Muramatsu, K. Takeda, K. Hashimoto, K. Amaya

Sci. & Tech. of High Pressure ( 5 ) 223 - 226 2000年

Two gaps in (VO)(2)P2O7: Observation using high-field magnetization and NMR 査読

T Yamauchi, Y Narumi, J Kikuchi, Y Ueda, K Tatani, TC Kobayashi, K Kindo, K Motoya

PHYSICAL REVIEW LETTERS 83 ( 18 ) 3729 - 3732 1999年11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：AMERICAN PHYSICAL SOC

The alternating one-dimensional Heisenberg S = 1/2 chain compound with spin gap, (VO)(2)P2O7, has been studied by the high-field magnetization and P-31 NMR measurements. Two critical phenomena at 25 +/- 1 and 46 +/- 2 T are observed in the magnetization curve, which are considered to be a crossover between the ground state and the excited state in two kinds of gap systems. P-31 NMR also revealed the coexistence of two magnetic systems with independent spin gaps. Results obtained from the present and previous studies are well explained by the model in which two kinds of magnetic chains along the b axis behave as alternating spin chains with independent gap energies.

DOI： 10.1103/PhysRevLett.83.3729

Field-induced 3D-LRO of Haldane-gap antiferromagnet NDMAZ 査読

A Koda, TC Kobayashi, K Amaya, H Yamashita

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 196 443 - 445 1999年5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

The heat capacity and magnetization measurements of the single crystal of Haldane-gap antiferromagnet NDMAZ were carried out at low temperatures down to 0.1 K and under magnetic fields up to 14 T. We have observed three-dimensional long-range ordering of NDMAZ at around T similar or equal to 0.3 K above H similar or equal to 13 T (H parallel to c), which is ascribed to both the field-induced gap quenching and the existence of finite interchain interaction. Applying the higher external held, the transition temperature reaches up to 0.6 K at H = 14 T, showing a negative curvature with respect to the external field. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(98)00804-X

Magnetic and transport properties of CeRh2Si2 under high pressures 査読

T Muramatsu, S Eda, TC Kobayashi, MI Eremets, K Amaya, S Araki, R Settai, Y Onuki

PHYSICA B-CONDENSED MATTER 259-61 61 - 62 1999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 SCIENCE BV

Magnetic and transport properties have been investigated in the single crystal of CeRh2Si2 under high pressures. We found that the magnetic susceptibility under high pressure shows a broad maximum like CeRu2Si2. In the present pressure range up to 13 kbar where the ordered state is suppressed, no obvious evidence of the superconducting transition is observed down to 50 mK. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00909-0

Metallization and superconductivity in CsI at pressures up to 220 GPa 査読

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

Journal of Physics Condensed Matter 10 ( 49 ) 11519 - 11523 1998年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The pressure range for electrical transport measurements has been dramatically increased up to 220 GPa in the 0.05-300 K temperature region and at magnetic fields of up to 10 T. Metallization of caesium iodide was found at a pressure of 115 GPa. A superconducting transition with T c = 2 K was observed above 180 GPa. T c decreases with increasing pressure. The superconducting transition shifts to lower temperatures and disappears under magnetic field above 0.3 Tesla.

DOI： 10.1088/0953-8984/10/49/037

Observation of pressure-induced superconductivity in the megabar region 査読

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

Journal of Physics Condensed Matter 10 ( 49 ) 11179 - 11190 1998年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

A review of recent developments in high-pressure techniques and their application in the search for superconductivity at low temperature is presented. We have focused the discussion mainly on the experimental results obtained by our group for simple molecular systems.

DOI： 10.1088/0953-8984/10/49/008

Orbital Frustration and Resonating Valence Bond State in the Spin-1/2 Triangular Lattice LiNiO 2 査読

Kitaoka Yoshio, Kobayashi Tatsuo, Koda Akihiro, Wakabayashi Hayato, Niino Yoshihiro, Yamakage Hirokazu, Taguchi Shinichiro, Amaya Kiichi, Yamaura Kazunari, Takano Mikio, Hirano Atushi, Kanno Ryoji

Journal of the Physical Society of Japan 67 ( 11 ) 3703 - 3706 1998年11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

From the 7Li nuclear magnetic resonance (NMR) and specific heatmeasurements of LiNiO2, consisting of a spin-1/2 triangular lattice, itis demonstrated that the previously suggested spin-glass-like freezingbelow Tsg=8 K, which is caused by defects of Li ions, is not the trueground state, but rather a quantum disordered state is realized without aspin gap. This state is characterized by power-law behavior of thetemperature dependence of the specific heat below 0.5 K. A spin-liquidstate with short-range ferromagnetic correlations is suggested from newinsight into the frustration of orbital ordering for doubly degenerateeg shells in the triangular lattice.

DOI： 10.1143/JPSJ.67.3703

Metallic CsI at Pressure of up to 220 Gigapascals 査読

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

Science 1998年4月

Enhancement of superconducting transition temperature in CeCu2Ge2 under high pressures 査読

T. C. Kobayashi, T. Miyazu, N. Takeshita, K. Shimizu, K. Amaya, Y. Kitaoka, Y. Onuki

J. Phys. Soc. Jpn. 67 ( 3 ) 996 - 999 1998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

Enhancement of superconducting transition temperature T c is confirmed at around 16 GPa in the pressure-induced superconductor CeCu2Ge2.The superconducting Hc-T c phase diagrams at the low-T c and high-T c pressure regions indicates that the heavy quasi particles form the singlet Cooper pairs.At both low-T c and high-T c pressure regions, Fermi liquid behavior of ρ∼ AT2 is observed only at low temperatures below 1 K in the normal state induced by the external field above Hc2.At 21 GPa where the superconductivity disappears down to 50 mK, the temperature region following ρ∼ AT2 increases drastically up to 40 K and the coefficient A decreases rapidly.These results indicate that the strongly correlated electrons are responsible essentially for the appearance of superconductivity in this system.

DOI： 10.1143/JPSJ.67.996

Magnetic-to-nonmagnetic transition in the ferromagnetic heavy-fermion compound CeRu2Ge2 at high pressures 査読

T. C. Kobayashi, T. Miyazu, K. Shimizu, K. Amaya, Y. Kitaoka, Y. Onuki, M. Shirase, T. Takabatake

Phys. Rev. B 57 ( 9 ) 5025 - 5028 1998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：American Physical Society

A zero-temperature magnetic-to-nonmagnetic transition has been investigated in the heavy-fermion ferromagnet CeRu2Ge2 from electrical-resistance measurements at pressures up to 15 GPa and temperatures down to 60 mK. We found that the magnetic-to-nonmagnetic phase boundary exists at around Pc∼10 GPa. The resistivity shows the quadratic temperature variation expected for the conventional Fermi liquid at low temperatures near Pc. In the present pressure range, neither the metamagnetic nor the superconducting transition was observed at least down to 60 mK.

DOI： 10.1103/PhysRevB.57.5025

Phase diagram of a new spin-Peierls compound: p-CyDOV 査読

T. Hamamoto, Y. Narumi, K. Kindo, K. Mukai, Y. Shimobe, T. C. Kobayashi, T. Muramatsu, K. Amaya

Physica B 246 36 - 39 1998年

Magnetic Properties of Oxygen Physisorbed in Cu-Trans-1,4-Cyclohexanedicarboxylic Acid 査読

Wasuke Mori, Tatsuo C. Kobayashi, Junji Kurobe, Kuichi Amaya, Yasuo Narumi, Takayuki Kumada, Koichi Kindo, Hiroko Aruga Katori, Tuneaki Goto, Noboru Miura, Satoshi Takamizawa, Hirokazu Nakayama, Kizashi Yamaguchi

Molecular Crystals and Liquid Crystals 306 1 - 7 1997年10月

Observation of weak ferromagnetism in organic verdazyl radical crystal, p-CyDpTV 査読

Kazuo Mukai, Masaaki Nuwa, Tomonari Morishita, Takaki Muramatsu, Tatsuo C. Kobayashi, Kiichi Amaya

Chemical Physics Letters 272 ( 5-6 ) 501 - 505 1997年7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

Magnetic property of 3-(4-cyanophenyl)-1,5-diphenyl-6-thioxoverdazyl (p-CyDpTV) radical crystal has been studied in the temperature range of 0.05-300 K in external magnetic fields 3, 11, 30, and 100 Oe by using SQUID magnetometer. Weak ferromagnetic behavior was observed at TN = 0.41 K. Below TN, the spontaneous magnetization Ms(T) increased rapidly, reaching a maximum of 31.1 emu/mol at 0.05 K. Spin-canting angle was estimated to be 0.32° at 0.05 K. Near TN, Ms(T) α [1-(T/TN)]β with the critical exponent of β = 0.36, in agreement with that expected for an isotropic three-dimensional (3D) Heisenberg spin system. © 1997 Elsevier Science B.V.

DOI： 10.1016/S0009-2614(97)00529-0

Magnetic Properties of One-Dimensional Heisenberg Chains with Ferromagnetic-Antiferromagnetic Bond Alternation 査読

M. Hagiwara, Y. Narumi, K. Kindo, T. C. Kobayashi, H. Yamakage, K. Amaya, G. Schmauch

Journal of the Physical Society of Japan 66 ( 6 ) 361 - 364 1997年6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

We report the results of susceptibility and magnetization measurements on ferromagnetic-antiferromagnetic alternating chain compounds [Cu(TIM)]CuCl4 (TIM=2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo-1,4,8,11-tetraazatetradecane) and (4-BzpipdH)CuCl3 (4-BzpipdH=4-benzylpiperidinium). Magnetization curves of both compounds are compared to those calculated for an S=1 linear-chain Heisenberg antiferromagnet. From the fitting of susceptibility data to a numerical formula calculated for an S=1/2 ferromagnetic-antiferromagnetic alternating chain [Inog. Chem. 33 (1994) 5171], we have estimated theantiferromagnetic exchange constant J AF/k B=2.9 K, the ferromagnetic exchange constant |J F|/k B=4.7 K and the g-value of the magnetic moment g=2.06 for the former and J AF/k B=8.8 K, |J F|/k B=38.8 K and g=2.17 for the latter, which are different from the values reportedpreviously.

DOI： 10.1143/JPSJ.66.1792

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

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

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

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

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.

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

その他リンク： https://jlc.jst.go.jp/DN/JALC/00223217421?from=CiNii

MAGNETIC PHASE-DIAGRAM IN (LA1-XBAX)2CUO4 査読

Y KITAOKA, K ISHIDA, T KOBAYASHI, K AMAYA, K ASAYAMA

PHYSICA C 153 733 - 734 1988年6月

Anisotropic Energy Gap of Strong Electron-Phonon Coupling Superconductor HfV2 査読

Yoshio Kitaoka, Yutaka Kishimoto, Tatsuo Kobayashi, Kiichi Amaya, Kunisuke Asayama

Japanese Journal of Applied Physics 26 ( 3-2 ) 1253 - 1254 1987年

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