竹内 哲也*; 屋良 朝之*; 安次富 洋介*; 伊覇 航*; 垣花 将司*; 中島 美帆*; 天児 寧*; 本多 史憲*; 本間 佳哉*; 青木 大*; et al.
Journal of the Physical Society of Japan, 87(7), p.074709_1 - 074709_14, 2018/07
Effects of magnetic field and pressure on the Kondo-like behavior in the valence-fluctuating antiferromagnetic compound EuPtSi were studied using single-crystalline samples. Anomalous features in EuPtSi are due to valence fluctuation and/or valence change of the Eu ions at low temperatures.
筒井 智嗣*; 金子 耕士; Pospisil, J.; 芳賀 芳範
Physica B; Condensed Matter, 536, p.24 - 27, 2018/05
Inelastic X-ray scattering (IXS) experiments of RTAl ( = La Ce, = Cu, Au) were carried out at 300 and 5.5 K. The spectra between LaCuAl and CeCuAl (LaAuAl and CeAuAl) are nearly identical at both temperatures except for temperature factors such as temperature dependence of Bose factor in IXS spectra and effect on thermal expansion. This means that no evident temperature dependence of IXS spectra was observed in CeTAl ( = Cu, Au).
松本 裕司*; 芳賀 芳範; 立岩 尚之; 山本 悦嗣; Fisk, Z.*
Journal of the Physical Society of Japan, 87(2), p.024706_1 - 024706_4, 2018/02
Single crystal samples of UPtIn with the hexagonal structure are grown from indium flux. Strong uniaxial magnetic anisotropy is revealed from magnetic property measurements. Specific heat measurement reveals a significant deviation from -linear behavior, indicating the smaller electronic specific heat than the previous study.
立岩 尚之; Pospisil, J.*; 芳賀 芳範; 山本 悦嗣
Physical Review B, 97(6), p.064423_1 - 064423_10, 2018/02
強磁性体URhAlの磁気臨界現象を研究した。自発磁化の臨界指数、磁化率の指数、強磁性転移温度における磁化の臨界指数を求めた。それぞれ=0.2870.005, =1.470.02, =6.080.04と決定された。これらの臨界指数はWidomのスケーリング則()を満たしている。得られた結果は、二次元イジングモデルについての繰り込み群を用いた理論モデルで説明される。
黒田 健太*; 越智 正之*; 鈴木 博之*; 平山 元昭*; 中山 光大*; 野口 亮*; Bareille, C.*; 明比 俊太朗*; 國定 聡*; 室 隆桂之*; et al.
Physical Review Letters, 120(8), p.086402_1 - 086402_6, 2018/02
We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit coupling (SOC), we draw the topological phase diagram of CeX and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion.
服部 泰佑; 酒井 宏典; 徳永 陽; 神戸 振作; 松田 達磨*; 芳賀 芳範
Physical Review Letters, 120(2), p.027001_1 - 027001_5, 2018/01
In order to identify the spin contribution to superconducting pairing compatible with the so-called "hidden order", Si nuclear magnetic resonance measurements have been performed using a high-quality single crystal of URuSi. A clear reduction of the Si Knight shift in the superconducting state has been observed under magnetic field applied along the crystalline axis, corresponding to the magnetic easy axis. These results provide direct evidence for the formation of spin-singlet Cooper pairs. Consequently, results indicating a very tiny change of in-plane Knight shift reported previously demonstrate extreme uniaxial anisotropy for the spin susceptibility in the hidden order state.
Pospisil, J.; 芳賀 芳範; 中島 邦久; 石川 法人; Csaov, I.*; 立岩 尚之; 山本 悦嗣; 山村 朝雄*
Solid State Communications, 268, p.12 - 14, 2017/12
A new compound of the composition ScPdAl showing polymorphism has been discovered. At room temperature, it crystalizes in the orthorhombic structure, but it transforms into a cubic phase above 1053C. ScPdAl exists as a very stable intermetallic phase just in the vicinity of the icosahedral quasicrystal AlPdSc.
藤森 伸一; 小畠 雅明; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 松本 裕司*; 山本 悦嗣; 立岩 尚之; et al.
Physical Review B, 96(12), p.125117_1 - 125117_9, 2017/09
The Fermi surface and band structure of have been studied by angle resolved photoelectron spectroscopy (ARPES) with the incident photon energies of = 665-735 eV. Detailed band structure and the three-dimensional shape of the Fermi surface were derived experimentally, and they are quantitatively explained by the band-structure calculation based on the density functional approximation. Comparison of the experimental ARPES spectra of with those of shows that they have considerably different spectral profiles particularly in the energy range of - 1 eV. Some energy bands with their energy dispersions of about 1 eV observed in are missing in the ARPES spectra of measured along the same high symmetry line of Brillouin zone, suggesting that U 5 states form these bands in . The relationship between the ARPES spectra of and is very different from the case between and where their intrinsic difference is limited only in the very vicinity of the Fermi energy. The present result argues that the U 5 electrons in have strong hybridization with ligand states, and essentially have an itinerant character.
藤森 伸一; 小畠 雅明; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*
Physical Review B, 96(11), p.115126_1 - 115126_10, 2017/09
The electronic structures of U (=Al, Ga, and In) were studied by photoelectron spectroscopy to understand the the relationship between their electronic structure and magnetic properties. The band structures and Fermi surfaces of UAl and UGa were revealed experimentally by angle-resolved photoelectron spectroscopy (ARPES), and they were compared with the result of band structure calculations. The topologies of the Fermi surfaces and the band structures of UAl and UGa were explained reasonably well by the calculation, although bands near the Fermi level () were renormalized owing to the finite electron correlation effect. The topologies of the Fermi surfaces of UAl and UGa are very similar to each other, except for some minor differences. Such minor differences in their Fermi surface or electron correlation effect might take an essential role in their magnetism.
Kim, H.*; 吉田 靖雄*; Lee, C.-C.*; Chang, T.-R.*; Jeng, H.-T.*; Lin, H.*; 芳賀 芳範; Fisk, Z.*; 長谷川 幸雄*
Science Advances (Internet), 3(9), p.eeao0362_1 - eeao0362_5, 2017/09
We report a first, real-space, imaging of an orbital ordered structure on a cobalt-terminated surface of the well-studied heavy fermion compound CeCoIn. Within small tip-sample distances, the cobalt atoms on a cleaved (001) surface take on dumbbell shapes alternatingly aligned in the  and  directions in scanning tunneling microscopy topographies. First-principles calculations reveal that this staggered orbital order is triggered by enhanced on-site Coulomb interaction at the surface.
芳賀 芳範; 松本 裕司*; Pospisil, J.; 立岩 尚之; 山本 悦嗣; 山村 朝雄*; Fisk, Z.*
Journal of Physics; Conference Series, 807(1), p.012015_1 - 012015_4, 2017/04
Transport characteristics of an antiferromagnetic uranium compound URhIn are studied. The antiferromagnetic transition leads to a formation of a gap on the Fermi surface as demonstrated by a hump in the resistivity behavior as a function of temperature. Hall effect, magnetoresistance and de Haas-van Alphen study consistently demonstrate a small carrier concentration in the antiferromagnetic state suggesting that majority of the Fermi surface vanishes.
Pospisil, J.; 郷地 順*; 芳賀 芳範; 本多 史憲*; 上床 美也*; 立岩 尚之; 神戸 振作; 長崎 尚子*; 本間 佳哉*; 山本 悦嗣
Journal of the Physical Society of Japan, 86(4), p.044709_1 - 044709_6, 2017/04
The effect of hydrostatic pressure on the electronic state of the antiferromagnet UIrGe is reported. A series of resistivity measurements up to 15 GPa demonstrated the Neel temperature decreases with increasing pressure and vanishes around 12 GPa. The transition from antiferromagnetic to paramagnetic phase appears to be of first order. A moderate increase in the effective mass was detected in the vicinity of the critical pressure.
Pospisil, J.; 芳賀 芳範; 神戸 振作; 徳永 陽; 立岩 尚之; 青木 大*; 本多 史憲*; 仲村 愛*; 本間 佳哉*; 山本 悦嗣; et al.
Physical Review B, 95(15), p.155138_1 - 155138_15, 2017/04
We investigated the evolution of magnetism in UIrRhGe system by systematic study on high-quality single crystals. We find a field-induced first order transition in the vicinity of the critical magnetic field along the axis in the entire UIrRhGe system, including the ferromagnetic region.
松本 裕司*; 芳賀 芳範; 立岩 尚之; 青木 晴善*; 木村 憲彰*; 山村 朝雄*; 山本 悦嗣; 松田 達磨*; Fisk, Z.*; 山上 浩志*
Journal of the Physical Society of Japan, 85(10), p.104709_1 - 104709_7, 2016/10
dHvA oscillations were detected on an actinide compound ThRuSi which is regarded as a reference to strongly correlated electron systems URuSi and CeRuSi. Observed Fermi surfaces well coincides with the band structure calculations, as well as experimentally obtained ones for a heavy fermion compound CeRuSi. On the other hand, Fermi surfaces of URuSi have significantly different characteristics, suggesting an itinerant ground state of 5f electrons.
服部 泰佑; 酒井 宏典; 徳永 陽; 神戸 振作; 松田 達磨*; 芳賀 芳範
Journal of the Physical Society of Japan, 85(7), p.073711_1 - 073711_4, 2016/07
藤森 伸一; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦
Journal of the Physical Society of Japan, 85(6), p.062001_1 - 062001_33, 2016/06
The electronic structures of uranium-based compounds are studied by photoelectron spectroscopies with soft X-ray synchrotron radiation. Angle-resolved photoelectron spectroscopy with soft X-rays made it possible to directly observe their bulk band structures and Fermi surfaces. It is shown that the band structure and Fermi surface of itinerant compounds are quantitatively explained by the band-structure calculation treating all U 5 electrons as being itinerant. Furthermore, the overall electronic structures of heavy Fermion compounds are also explained by the band-structure calculation although there exist some disagreements which might be originated from the electron correlation effect. This suggests that the itinerant description of U states is an appropriate starting point for their description. The local electronic structures of uranium site are probed by the core-level photoelectron spectroscopy with soft X-rays. The comparisons of core-level spectra of these compounds with typical itinerant and localized compounds suggest that the local electronic structures of most of itinerant and heavy Fermion compounds are close to U 5 configuration.
郷地 順*; 住山 昭彦*; 山口 明*; 本山 岳*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦
Physical Review B, 93(17), p.174514_1 - 174514_5, 2016/05
The Josephson effect between a single crystal UPt and a conventional superconductor Al has been investigated under pressure. A possible change of the superconducting order parameter has been detected at a critical where the symmetry-breaking antiferromagnetic order disappears. The conclusion is also supported by the different behaviors observed in Josephson current and penetration depth.
藤森 伸一; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦
Journal of Electron Spectroscopy and Related Phenomena, 208, p.105 - 110, 2016/04
橘高 俊一郎*; 清水 悠晴*; 榊原 俊郎*; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦; 堤 康雅*; 野本 拓也*; 池田 浩章*; 町田 一成*
Journal of the Physical Society of Japan, 85(3), p.033704_1 - 033704_4, 2016/03
Low-energy quasiparticle excitations in the heavy-fermion superconductor URuSi were investigated by specific heat measurements as a function of temperature, magnetic field and its angle. Experimental results agree with the theoretical model for a superconducting gap with chiral -wave symmetry.
Pospisil, J.; Opletal, P.*; Valika, M.*; 徳永 陽; Stunault, A.*; 芳賀 芳範; 立岩 尚之; Gillon, B.*; 本多 史憲*; 山村 朝雄*; et al.
Journal of the Physical Society of Japan, 85(3), p.034710_1 - 034710_10, 2016/03
We have investigated the ferromagnetic (FM) phase, which suddenly develops in UCoRuAl and is isolated by paramagnetic regions on both sides from the parent UCoAl and URuAl. We conclude that both criticalities are influenced by disorder. Criticality on the UCoAl side has character of a clean FM metal, while on the Ru rich side it has the character of a magnetically inhomogeneous system involving a Griffiths phase.