川崎 郁斗; 小畠 雅明; 藤森 伸一; 竹田 幸治; 山上 浩志; 仲村 愛*; 伊覇 航*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*
Journal of the Physical Society of Japan, 89(4), p.044704_1 - 044704_6, 2020/04
EuPd is a rare Eu-based compound, whose Eu ions are in a trivalent state. The electronic structure of EuPd was investigated by angle-resolved photoemission spectroscopy (ARPES) using soft X rays. Eu components arising from the 4f final state multiplet were clearly observed in the valence spectra, and no Eu components were observed within an experimental accuracy, confirming a robust Eu state. The band structure and Fermi surfaces revealed by ARPES measurements were compared to the band structure calculations based on the density-functional theory for LaPd andYPd. We found that the calculation for LaPd provides a better description for our ARPES results. The effective electron masses estimated from the ARPES spectra near the Fermi level are in good agreement with the corresponding cyclotron effective masses in previous de Haas-van Alphen experiments.
竹内 徹也*; 芳賀 芳範; 谷口 年史*; 伊覇 航*; 安次富 洋介*; 屋良 朝之*; 木田 孝則*; 田原 大夢*; 萩原 政幸*; 中島 美帆*; et al.
Journal of the Physical Society of Japan, 89(3), p.034705_1 - 034705_15, 2020/03
Single crystals of EuCuSi have been grown by the flux method and Bridgman method. The Eu ions of the Bridgman-grown crystal are nearly trivalent and fluctuate depending on the temperature. On the other hand, the Eu ions of flux-grown sample are divalent and thermally stable and show spin-glass behavior at low temperatures. Crystallographic analyses identified random replacement of Cu sites by Si only for the flux-grown samples. Such structural randomness leads to spin-glass features.
大貫 惇睦*; 垣花 将司*; 伊覇 航*; 仲井間 憲李*; 青木 大*; 仲村 愛*; 本多 史憲*; 中島 美帆*; 天児 寧*; 郷地 順*; et al.
JPS Conference Proceedings (Internet), 29, p.012001_1 - 012001_9, 2020/02
EuPtSi with the cubic chiral structure exhibits a skyrmion phase under magnetic field. We succeeded in growing high-quality single crystals by the Bridgman method. Fermi surface splitting reflecting the noncentrosymmetric structure was successfully observed experimentally.
金子 耕士; 垣花 将司*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*
固体物理, 54(12), p.757 - 766, 2019/12
田端 千紘*; 松村 武*; 中尾 裕則*; 道村 真司*; 垣花 将司*; 稲見 俊哉*; 金子 耕士; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*
Journal of the Physical Society of Japan, 88(9), p.093704_1 - 093704_5, 2019/09
The magnetic order in the magnetic-fild-induced so-called A phase of cubic chiral antiferromagnet EuPtSi was investigated by resonant X-ray scattering (RXS) near the Eu edge. The high flux RXS signal under the magnetic field applied along  revealed the first and second order satellite magnetic reflections, indicating that the A phase is a triple- magnetic ordered state that is described by three propagation vectors lying in the plane normal to the magnetic field direction; , , and . With the high resolution in the reciprocal space achieved in the RXS measurement, it is suggested that the triple- order strongly couples with the underlying crystal lattice. The triple- magnetic order is discussed in the context of a magnetic skyrmion lattice on which the geometrical frustration may play a crucial role.
川崎 郁斗; 藤森 伸一; 竹田 幸治; 山上 浩志; 伊覇 航*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*
Physical Review B, 100(3), p.035111_1 - 035111_8, 2019/07
We have carried out angle-integrated photoemission spectroscopy (AIPES) and angle-resolved photoemission spectroscopy (ARPES) experiments using soft X-rays on single crystals of EuCuGe and EuCuSi grown by the Bridgman method to investigate their electronic structures. The AIPES results showed that the Eu ions in EuCuGe and EuCuSi are in a divalent state and a nearly trivalent state, respectively, in accord with the previously reported magnetic properties. The three-dimensional band structures and shapes of the Fermi surfaces of EuCuGe and EuCuSi were studied by ARPES measurements. We found that the band structures near the Fermi level and Fermi surfaces of EuCuGe and EuCuSi are very different from each other and are well reproduced by the band structure calculations based on density-functional theory for SrCuGe and YCuSi. This suggests that a charge transfer from the localized 4 states into the valence bands is responsible for the difference in the electronic states between EuCuGe and EuCuSi.
伊覇 航*; 垣花 将司*; 松田 進弥*; 本多 史憲*; 芳賀 芳範; 竹内 徹也*; 中島 美帆*; 天児 寧*; 郷地 順*; 上床 美也*; et al.
Journal of Alloys and Compounds, 788, p.361 - 366, 2019/06
Ferromagnetic ordering of EuCuP is investigated on a single crystal sample grown from tin flux. Application of hydrostatic pressure up to 8 GPa stabilizes ferromagnetic ordering, suggesting divalent Eu is stable. The Hall effect and resistivity measurements show that EuCuP is a low-carrier ferromagnetic metal with a characteristic resistivity cusp appearing at the ferromagnetic transition temperature.
青山 泰介*; 小手川 恒*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦*; 藤 秀樹*
Journal of the Physical Society of Japan, 88(6), p.064706_1 - 064706_7, 2019/06
Pt-NMR measurements under magnetic field () parallel to the -axis in the vicinity of the upper critical field have been carried out on the heavy-fermion superconductor UPt. The quasiparticle spin susceptibility was obtained from the measurements. The field dependence of the susceptibility suggests that the -vector freely rotates in magnetic field. It is therefore concluded that spin-orbit interaction, which confines the direction of the -vector with respect to the crystal axis, is weak in UPt.
金子 耕士; Frontzek, M. D.*; 松田 雅昌*; 中尾 朗子*; 宗像 孝司*; 大原 高志; 垣花 将司*; 芳賀 芳範; 辺土 正人*; 仲間 隆男*; et al.
Journal of the Physical Society of Japan, 88, p.013702_1 - 013702_5, 2019/01
Magnetic transitions in chiral antiferromagnet EuPtSi were investigated by means of single crystal neutron diffraction. In the ground state, magnetic peaks emerge at positions represented by =. Upon heating, an additional magnetic peak splitting around 2.5 K was uncovered, indicating a presence of a first-order transition with =. An half-polarized neutron scattering for polarization parallel to Q reveled that polarization antiparallel to Q has stronger intensity in both magnetic phases. This feature clarifies single chiral character of helical structure with moments normal to the ordering vector in both ordered states. Under vertical magnetic field along [1,1,1] in the phase, magnetic peaks form hexagonal patterns in the equatorial scattering plane around nuclear. An ordering vector of the -phase has the similar size in the periodicity to , and could be a hallmark of a formation of skyrmion lattice in EuPtSi.
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, 99(3), p.035109_1 - 035109_5, 2019/01
In the present study, we have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the 4-5 resonant photoemission spectroscopy. Obtained pDOS exhibit a systematic trend depending on the physical properties of compounds: Although the coherent peak at the Fermi level can be explained by the band-structure calculation, an incoherent peak emerges on the higher binding energy side () in the cases of localized and heavy fermion compounds. The intensity and energy position of the incoherent peak is increased and shifted to a higher binding energy as the localization of the state increases. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard- type mechanism takes an essential role in the electronic structure of actinide materials.
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*
Progress in Nuclear Science and Technology (Internet), 5, p.82 - 85, 2018/11
One of the most remarkable properties of actinide compounds is the coexistence of superconductivity and magnetic ordering which has been realized in several strongly-correlated uranium based compounds. In these compounds, both superconductivity and magnetic ordering originate from U 5f states. To understand the origin of the coexistence as well as the mechanism of the superconductivity, it is essential to reveal their U 5f electronic structures. In this presentation, the U 5f electronic structures of heavy Fermion superconductors UPdAl and URuSi studied by photoelectron spectroscopy using soft X-rays from SPring-8 BL23SU are presented. For UPdAl, U 4d-5f resonant photoemission experiment was performed, and its partial U 5f spectrum was revealed experimentally. Furthermore, we have applied the three-dimentional ARPES to the hidden order compound URuSi, and revealed its complete 3D electronic structure in the paramagnetic phase. Their electronic structures are discussed based on these results.
竹内 徹也*; 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.
伊覇 航*; 屋良 朝之*; 安次富 洋介*; 垣花 将司*; 竹内 徹也*; 本多 史憲*; 仲村 愛*; 青木 大*; 郷地 順*; 上床 美也*; et al.
Journal of the Physical Society of Japan, 87(6), p.064706_1 - 064706_14, 2018/06
We succeeded in growing single crystals of the series of EuCu(GeSi) compounds.Physical property measurements demonstrate a maximum of the antiferromagnetic transition temperature appears at . Antiferromagnetism then disappears around followed by a heavy-fermion formation at higher concentrations. These observations follow the Doniach phase diagram as a function of .
竹田 幸治; 斎藤 祐児; 岡根 哲夫; 山上 浩志; 松田 達磨*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦*
Physical Review B, 97(18), p.184414_1 - 184414_7, 2018/05
We have performed soft X-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U 4-5 () and Co 2-3 () absorption edges in order to investigate the magnetic properties of the U 5 and Co 3 electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co 3 electrons is unusually large. Through the systematic temperature ()- and magnetic field ()-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of and (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was observed clearly under 15 K at . The value of the and its -dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings show clearly that the role of the Co 3 electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.
野間 雄一郎*; 小手川 恒*; 久保 徹郎*; 藤 秀樹*; 播磨 尚朝*; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*; 伊藤 公平*; Haller, E. E.*; et al.
Journal of the Physical Society of Japan, 87(3), p.033704_1 - 033704_5, 2018/03
Ge nuclear quadrupole resonance study of ferromagnetic superconductor UGe is reported. Detailed analyses successfully assigned crystallographic sites of Ge atoms. The measurement of the nuclear spin-lattice relaxation rate revealed highly anisotropic magnetic fluctuations.
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.
川崎 卓郎; 金子 耕士; 仲村 愛*; 阿曽 尚文*; 辺土 正人*; 仲間 隆男*; 大原 高志; 鬼柳 亮嗣; 及川 健一; 田村 格良; et al.
Journal of the Physical Society of Japan, 85(11), p.114711_1 - 114711_5, 2016/11
The magnetic structure of the intermetallic compound EuGa was investigated using single-crystal neutron diffraction with TOF Laue technique on the new diffractometer SENJU at MLF of J-PARC. Despite of the high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections appeared at 2 below 16 K, indicating that the ordering vector is = (0, 0, 0). The continuous evolution of the magnetic reflection intensity below T follows a squared Brillouin function for = 7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa revealed that a nearly full magnetic moment of 6.4 B of Eu lies within the basal plane of the lattice.
小畠 雅明; 藤森 伸一; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 小林 啓介*; 山上 浩志; 仲村 愛*; 辺土 正人*; 仲間 隆男*; et al.
Journal of the Physical Society of Japan, 85(9), p.094703_1 - 094703_6, 2016/09
The electronic structure of a divalent compound EuAl, which shows the charge density wave transition at , was studied by the hard X-ray angle-integrated photoelectron spectroscopy (HAXPES) and the soft X-ray angle resolved photoelectron spectroscopy (ARPES). The valence band and core-level spectra obtained by the HAXPES are consistent with the divalent nature of Eu atoms in EuAl. Furthermore, the Fermi surface as well as the band structure in the vicinity of the Fermi Energy () of EuAl are very similar to those of its isostructural divalent compound SrAl, which does not have electrons. These suggest that Eu atoms are divalent in EuAl, and electrons are completely localized with electronic configuration in the ground state. The ARPES spectra measured along the --Z high-symmetry line did not show significant temperature dependences above and below within the energy resolution of . Moreover, the Fermi surface mapping along the direction showed that both of EuAl and SrAl have highly three-dimensional electronic structures, suggesting that the nesting of Fermi surface is not straightforward. The Fermi surface and band structure of SrAl were well explained by the band-structure calculation based on the local density approximation.
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.