研究者詳細 - 小林　達生

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

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

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

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

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