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常盤 欣文; Opletal, P.; 酒井 宏典; 山本 悦嗣; 神戸 振作; 徳永 陽; 芳賀 芳範; 木俣 基*; 淡路 智*; 佐々木 孝彦*; et al.
no journal, ,
非従来型超伝導では、磁性が超伝導相互作用の起源と考えられており、磁性と超伝導の関係性は研究の中心的テーマとなっている。UTeは、磁場中でのリエントラント超伝導やスピン3重項超伝導の可能性などにより、多くの注目を集めている。この物質において、a軸方向に磁場を印可すると、6T付近でフェルミ面の不安定性による弱いメタ磁性が発生する。気相成長法で合成された初期の結晶では、
=1.6Kで上部臨界磁場
=6Tであったため、メタ磁性が発生する磁場では超伝導が消失しており、超伝導に影響はなかった。溶融塩フラックス法により合成された純良単結晶では、=2.1Kは当初のから25%増強であるのに対して、=12Tは2倍になっており、メタ磁性が超伝導に影響を与えうる。本研究では、このメタ磁性がを増強していることを明らかにした。
Pt
Al
芳賀 芳範; 山本 悦嗣; 松本 裕司*; 白崎 謙次*
no journal, ,
UPtAl is known as a uranium intermetallic compound with the hexagonal structure. Detailed crystal structure investigations revealed that uranium atoms form a honeycomb layer stacking along the c-axis. Two magnetic phase transitions were identified by thermodynamic measurements, suggesting a successive change in the magnetic structure.
-electron systems; X-ray magnetic circular dichroism study of BaCaOsO芝田 悟朗; 林 浩章*; 河村 直己*; 岡本 淳*; Huang, D. J.*; 田中 新*; Streltsov, S.*; 山浦 一成*; 藤森 淳*
no journal, ,
The double perovskite-type (DP) oxide BaCaOsO with 
electron configuration is one of the candidates for magnetic octupole order. In the present study, we investigated the Os 5 electronic structure of BaCaOsO polycrystals under magnetic fields via Os 
-edge hard X-ray magnetic circular dichroism (XMCD). In contrast to conventional XMCD spectra of 3 and 4 electron systems, relatively large (
%) XMCD signal was observed at the 
-edge, whereas it is weak (
%) at the 
edge, suggesting a large orbital magnetic moment due to the strong SOI of Os 5 electrons. The overall line shapes of the XAS and XMCD spectra can be simulated by atomic multiplet calculations with cubic symmetry. The calculations show that Coulomb interaction is weak compared to Os 5 SOI, suggesting that SOI plays an importance role in the electronic structure of BaCaOsO.
Opletal, P.; 酒井 宏典; 芳賀 芳範; 三宅 厚志*; 徳永 将史*; 常盤 欣文; 山本 悦嗣; 神戸 振作; 徳永 陽
no journal, ,
UOX (X = S, Se, Te) crystallizes in tetragonal PbFCl-type structure (P4/nmm space group). Only polycrystalline samples are reported in literature. UOS, UOSe and UOTe were reported to be antiferromagnets with T
= 55, 100 and 160 K, respectively. Magnetic structure of UOS and UOSe were reported to have moment along the c-axis with Q = (0,0,1/2). UOS and UOSe were both reported to exhibit semiconducting behavior on polycrystalline samples. UOTe was theoretically predicted to have nontrivial topology. We have prepared first single crystals of UOX (X = S, Se, Te) and shown they exhibit semimetallic conductivity and UOS exhibits increase of T by almost 30 K in contrast to published literature. We will present the method of preparation of single crystals, results of magnetic, transport, thermal measurements, all effect and data obtained in high magnetic fields. We will discuss these results in connection to Weyl semimetals and results published in literature and anisotrpy observed in electric resistivity.
-electron systems石飛 尊之
no journal, ,
This presentation focuses on partial ordering in frustrated systems. Partial orders typically arise as a three sublattice order in systems with frustration and Ising anisotropy. In this presentation, we present new mechanisms for stabilizing partial orders beyond Ising-type anisotropy. We show a partial quadrupole order with one-fourth disordered sites, stabilized by 
anisotropy unique to electric degrees of freedom. This partial order is robust at high temperatures within a framework of the Landau theory. This mechanism is an extension of the three-sublattice partial order with 
Ising anisotropy. We also discuss magnetic partial order mechanisms involving quadrupole moment interactions, where partial magnetic disorder persists even in quadrupole-ordered ground states. Finally, we examine a scenario with three partially magnetic ordered states due to quadrupole interactions, with potential applications to partially ordered state in UNi
B.
酒井 宏典; 常盤 欣文; Opletal, P.; 木俣 基*; 淡路 智*; 佐々木 孝彦*; 青木 大*; 神戸 振作; 徳永 陽; 芳賀 芳範
no journal, ,
溶融塩フラックス法を用いて、報告されている中で最も高い超伝導(SC)転移温度を持つ高品質なUTe単結晶を育成した。この結晶は、残留電子比熱が小さく、残留抵抗比が大きい。UTeのSC相図を調べ、低磁場と高磁場のSC相が対照的な磁場角依存性を持つことを明らかにした。また、中間的なSC状態も見いだされた。結晶の質によって低磁場超伝導相の上部臨界磁場が増加するにも関わらず、高磁場相が現れる磁場は約15Tで変化しない。MSF法により、このスピン三重項超伝導体の量子振動の観測とフェルミ面研究の進展があった。
角田 一樹
no journal, ,
Topological materials have attracted vast research interests due to their exotic physical properties. The peculiar electronic structures in these materials, such as Dirac-cone-like surface states (SS) in topological insulators, originate from the band inversion caused by spin-orbit coupling. Therefore, heavy-element compounds can be a good platform for searching the topologically non-trivial phases. Recently, the band inversion and Dirac-cone-like SS have been verified in rare-earth monopnictides utilizing angle-resolved photoelectron spectroscopy (ARPES). For actinide monopnictides, on the other hand, similar topological band structures were theoretically predicted, but few experimental investigations have been conducted. In this work, we have investigated the electronic structures of Th-based actinide monopnictides by first-principles calculations and observed the signature of band inversion in ThSb by soft X-ray ARPES.
藤森 伸一; 竹田 幸治; 山上 浩志; 山本 悦嗣; 芳賀 芳範; 川崎 郁斗
no journal, ,
UPt
shows a superconducting transition at Tc = 0.5 K, and the superconducting state has multiple phases in the magnetic-field and temperature plane, revealing the presence of multiple superconducting order parameters. The above superconducting state is formed by heavy quasiparticles. In this study, we performed angle-resolved photoemission (ARPES) experiments using soft X rays to investigate the electronic structure of the heavy-fermion superconductor UPt. The overall band structure revealed by the present ARPES measurements is compared with density-functional calculations for UPt and the non-5f reference compound ThPt. We showed that the calculation for ThPt gives a better description of ARPES results except for heavy quasiparticle bands at the Fermi level (EF). In addition, we extracted the U 5f spectral weight by utilizing photo energy dependence on the photoemission cross-section. In the soft X-ray range, the U 5f and Pt 5d orbitals have dominant contributions, and the relative photoemission cross-section ratio decreases with increasing photon energy, and therefore, we can extract the U 5f component by comparing the spectra measured at different photon energies. Figure 1 shows the ARPES spectra at the high-symmetry points measured at two different photon energies. The difference curves reflect the U 5f spectral function. The narrow peak located at EF, whose bandwidth is narrower than the present energy resolution, is the coherent heavy quasiparticle component. The difference curves in Fig. 1 revealed that most of the U 5f spectral weight exist not as the coherent heavy fermion bands but as incoherent components which distribute over a wide energy range from near EF region to 2 eV. Therefore, this result shows that the heavy quasiparticle bands are enormously renormalized by the electron correlation effect and is consistent with the reported heavy fermion behavior.
; A Perspective from photoelectron spectroscopy藤森 伸一; 川崎 郁斗; 竹田 幸治; 山上 浩志; 仲村 愛*; 本間 佳哉*; 青木 大*
no journal, ,
The unconventional superconductors in -based materials attract much attention in recent years. Recently, it was discovered that UTe has relatively high transition temperature, and it is classified into one of such class of materials. In the present study, the electronic structure of UTe was studied by resonant photoelectron spectroscopy (RPES) and angle-resolved photoelectron spectroscopy (ARPES) with soft X-ray synchrotron radiation. The partial U 5 density of states of UTe were imaged by the U 4-5 RPES and it was found that the U 5 state has an itinerant character, but there exists an incoherent peak due to the strong electron correlation effects. The band structure of UTe was obtained by ARPES and its overall band structure was mostly explained by band structure calculations, except for the incoherent band at 
eV. These results suggest that the U 5 states of UTe have itinerant but strongly-correlated nature with enhanced hybridization with the Te 5
states. The new ARPES data of the detailed electronic structure of Z point will be presented.
Si神戸 振作
no journal, ,
この研究では、Ru-NQRの正確な測定により、[100]および[110]方向に沿った一軸応力下の隠れ秩序状態におけるRuサイトの局所的対称性が決定された。これらの測定結果も、一軸応力のない隠れ秩序状態のRuサイトでの4回対称性を裏付けている。さらに、特定のケースは、以前に提案された可能なケースから除外される可能性がある。一軸測定と群理論的考察に基づく隠れ次数対称性の決定に関する議論をする。