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states in the electronic structure of the intermediate-valence superconductor CeIr
藤森 伸一; 川崎 郁斗; 竹田 幸治; 山上 浩志; 雀部 矩正*; 佐藤 芳樹*; 清水 悠晴*; 仲村 愛*; Maruya, A.*; 本間 佳哉*; et al.
Electronic Structure (Internet), 5(4), p.045009_1 - 045009_7, 2023/11
The electronic structure of the 
-based superconductor 
was studied by photoelectron spectroscopy. The energy distribution of the 
state was revealed by the 
resonant photoelectron spectroscopy. The state was mostly distributed in the vicinity of the Fermi energy, suggesting the itinerant character of the state. The contribution of the state to the density of states (DOS) at the Fermi energy was estimated to be nearly half of that of the
states, implying that the state has aconsiderable contribution to the DOS at the Fermi energy. The 
core-level and X-ray absorption spectra were analyzed based on a single-impurity Anderson model. The number of the state in the ground state was estimated to be 0.8-0.9, which is much larger than the values obtained in the previous studies (i.e., 0-0.4).
symmetry for anisotropic 
hybridization in the heavy-fermion superconductor CeNi
Ge藤原 秀紀*; 中谷 泰博*; 荒谷 秀和*; 金井 惟奈*; 山神 光平*; 濱本 諭*; 木須 孝幸*; 山崎 篤志*; 東谷 篤志*; 今田 真*; et al.
Physical Review B, 108(16), p.165121_1 - 165121_10, 2023/10
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)We report the ground-state symmetry of the Ce 4 states in the heavy-fermion superconductor CeNiGe, yielding anisotropic hybridization between the Ce 4 states and conducting electrons. By analyzing linear dichroism in soft X-ray absorption and core-level hard X-ray photoemission spectra, the 4 symmetry is determined as 
-type 
, promoting predominant hybridization with the conducting electrons originating from the Ge site. The band structures probed by soft X-ray angle-resolved photoemission indicates that the Ge 4
components contribute to the band renormalization through the anisotropic hybridization effects, suggesting that the control of the electronic structures of Ge orbital gives an impact to achieve the exotic phenomena in CeNiGe.
川崎 郁斗; 竹内 一陽*; 藤森 伸一; 竹田 幸治; 山上 浩志; 山本 悦嗣; 芳賀 芳範
Physical Review B, 108(16), p.165127_1 - 165127_9, 2023/10
被引用回数：1 パーセンタイル：0.00(Materials Science, Multidisciplinary)We performed angle-resolved photoemission spectroscopy (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-
reference compound ThPt. We showed that the calculation for ThPt gives a better description of the experimental band structure, except for the -derived heavy quasiparticle bands. This situation is reminiscent of Ce-based heavy-fermion systems, whose band structures are often very similar to those of non- La-based compounds. The narrow heavy quasiparticle bands are located just below the Fermi level (
), and their band structure could not be resolved by the present energy resolution. We also showed that most of the U spectral weight exists not as the coherent heavy-fermion bands but as incoherent components that distribute over a wide energy range, spanning from near to approximately 2 eV. This result indicates that the heavy quasiparticle bands are enormously renormalized by the electron correlation effect. Additionally, we showed that the spectral intensity of the heavy-fermion bands is almost temperature independent, at least up to 100 K, where the magnetic susceptibility follows a Curie-Weiss behavior.
竹田 幸治; Posp
il, J.*; 山上 浩志; 山本 悦嗣; 芳賀 芳範
Physical Review B, 108(8), p.085129_1 - 085129_10, 2023/08
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)We investigated the element-specific electronic states and magnetic properties of ferromagnetic superconductor UCoGe and Ru-substituted U(Co
Ru
)Ge using soft X-ray magnetic circular dichroism (XMCD) experiments. YCoGe, a nonmagnetic compound without the 5 electrons, was also examined as a reference material. The shapes of the XMCD spectra of UCoGe at the U 
and Ge 
edges are indistinguishably similar to those of U(CoRu)Ge. On the other hand, the XMCD spectral shape at the Co 
edge is very peculiar and is changed by the existence of the U 5 electrons and the Ru substitution. From the sum rule analysis for the XMCD spectra, it was found that the magnetic moments of the U 5 and Co 3
electrons in UCoGe and U(CoRu)Ge are aligned in the same direction under the present experimental conditions; 
= 5.5 - 50 K and 
= 0 - 10 T. Furthermore, even in the case of YCoGe, the Co 3 electrons have a large orbital magnetic moment, suggesting that the Co 3 electrons in these compounds are in a low symmetric electronic environment originally. Through the - and -dependence of the XMCD intensity, it was revealed that the magnetic properties at the Co site are not simply induced by the magnetism at the U site and that the Co 3 electrons play an important role in the stability of ferromagnetism.
localized ferromagnet CeRu
Ge studied by soft X-ray photoemission spectroscopy川崎 郁斗; 藤森 伸一; 竹田 幸治; 山上 浩志; 大貫 惇睦*
Journal of the Physical Society of Japan, 92(6), p.064709_1 - 064709_8, 2023/06
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)The electronic state of 4 localized ferromagnet CeRuGe has been investigated by angle-resolved photoemission spectroscopy (APRES) experiments using soft X rays. The band structure and Fermi surfaces consisting of non-4 bands are almost consistent with a calculation based on the density-functional theory for LaRuGe, thus confirming a localized character of the 4 electrons. On the other hand, the Ce 3-4 resonant ARPES experiments demonstrated that the 4 spectral function is dominated by 
components in the vicinity of the Fermi level and thus is different from that expected for a localized electron system. We also revealed that the intensities of the components have almost no temperature dependence up to at least 100 K, which is two orders of magnitude larger than the Kondo temperature of CeRuGe.
Rh
Sn
岩佐 和晃*; Suyama, Kazuya*; 河村 聖子; 中島 健次; Raymond, S.*; Steffens, P.*; Yamada, Akira*; 松田 達磨*; 青木 勇二*; 川崎 郁斗; et al.
Physical Review Materials (Internet), 7(1), p.014201_1 - 014201_11, 2023/01
被引用回数：4 パーセンタイル：34.64(Materials Science, Multidisciplinary)The spin dynamics, crystalline-electric-field (CEF) level scheme, specific heat, and X-ray photoemission spectra (XPS) of CeRhSn were investigated, which exhibits anomalous semimetal transport in the chiral crystallographic phase. CEF excitations observed at approximately 7 and 39 meV are consistent with the two inequivalent Ce-ion cites in the chiral structure. Because of broader CEF excitations and a strong 4 peak at the Fermi level in the Ce 4 on-resonance spectrum, the hybridized Ce 4 electrons contribute to the semimetal carriers. In addition, the spin fluctuation associated with the Kramers doublet ground state is characterized by the peak located at 0.15 meV. The electronic state involving the spin fluctuation causes the 
behavior of specific heat below 0.6 K, which is attributed to linear dispersion relations of electrons of the Weyl Kondo semimetal in the chiral-lattice symmetry.
Al; Impact of the U states on the electronic structure of UPdAl藤森 伸一; 竹田 幸治; 山上 浩志; Pospil, J.*; 山本 悦嗣; 芳賀 芳範
Physical Review B, 105(11), p.115128_1 - 115128_6, 2022/03
被引用回数：1 パーセンタイル：7.68(Materials Science, Multidisciplinary)The electronic structure of 
, which is isostructural to the heavy fermion superconductor 
, was investigated by photoelectron spectroscopy. The band structure and Fermi surfaces of were obtained by angle-resolved photoelectron spectroscopy (ARPES), and the results were well-explained by the band-structure calculation based on the local density approximation. The comparison between the ARPES spectra and the band-structure calculation suggests that the Fermi surface of mainly consists of the 
and 
states with a minor contribution from the 
states. The comparison of the band structures between and 
argues that the 
states form Fermi surfaces in through hybridization with the state in the 
layer, suggesting that the Fermi surface of has a strong three-dimensional nature.
P studied by soft X-ray photoemission spectroscopy川崎 郁斗; 小畠 雅明; 藤森 伸一; 竹田 幸治; 山上 浩志; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*
Physical Review B, 104(16), p.165124_1 - 165124_8, 2021/10
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)We carried out angle-resolved photoemission (ARPES) experiments using soft X rays to investigate the electronic structure of the intermediate valence compound EuNiP. Both the Eu
and Eu
components arising from the 4
and 4
final states were observed in the valence spectra, directly confirming an intermediate character of Eu ions. The three-dimensional band structure was studied by ARPES measurements, and we found that the ARPES spectra up to just below the Fermi level can well be explained by a calculation based on the density-functional theory for the non-4 reference compound SrNiP. The heavy-fermion bands in EuNiP are thus considered to be formed through the hybridization between the dispersive valence bands, which resemble those for SrNiP, and the Eu components located at the very vicinity of the Fermi level.
Si in paramagnetic phase; Three-dimensional angle resolved photoelectron spectroscopy study藤森 伸一; 竹田 幸治; 山上 浩志; 山本 悦嗣; 芳賀 芳範
Electronic Structure (Internet), 3(2), p.024008_1 - 024008_8, 2021/06
The three-dimensional (3D) electronic structure of the hidden order compound 
in a paramagnetic phase was revealed using a 3D angle-resolved photoelectron spectroscopy where the electronic structure of the entire Brillouin zone is obtained by scanning both incident photon energy and detection angles of photoelectrons. The quasi-particle bands with enhanced contribution from the state were observed near 
, formed by the hybridization with the 
states. The energy dispersion of the quasi-particle band is significantly depend on
, indicating that they inherently have a 3D nature. The band-structure calculation qualitatively explain the characteristic features of the band structure and Fermi surface although the electron correlation effect strongly renormalizes the quasi-particle bands. The 3D and strongly-correlated nature of the quasi-particle bands in is an essential ingredient for modeling its hidden-order transition.
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*
Journal of the Physical Society of Japan, 90(1), p.015002_1 - 015002_2, 2021/01
被引用回数：21 パーセンタイル：83.09(Physics, Multidisciplinary)The valence state of 
was studied by core-level photoelectron spectroscopy. The main peak position of the 
core-level spectrum of coincides with that of 
, which is anitinerant compound with a nearly 
configuration. However, the main peak of is broader than that of, and satellite structures are observed in the higher binding energy side of the main peak, which are characteristics of mixed-valence uranium compounds. These results suggest that the state in isin a mixed valence state with a dominant contribution from the itinerant configuration.
Mn
As via soft X-ray magnetic circular dichroism竹田 幸治; 大矢 忍*; Pham, N. H.*; 小林 正起*; 斎藤 祐児; 山上 浩志; 田中 雅明*; 藤森 淳*
Journal of Applied Physics, 128(21), p.213902_1 - 213902_11, 2020/12
被引用回数：8 パーセンタイル：39.80(Physics, Applied)In order to understand the mechanism of the ferromagnetism in GaMnAs ((Ga,Mn)As), we have investigated the magnetic behavior on a microscopic level through systematic temperature () and magnetic-field (
) dependent soft X-ray magnetic circular dichroism (XMCD) experiments at the Mn absorption edges. The and dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations and different Curie temperature (
) values. In particular, the SPM component develops well above , indicating that local FM regions are formed well above . The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families.
Orlandi, R.; 廣瀬 健太郎; 矢板 毅; 山上 浩志; 家田 淳一; 神戸 振作; 石川 法人
日本原子力学会誌ATOMO, 62(5), p.280 - 284, 2020/05
先端基礎研究センターで行っている研究を紹介する。(1)人工元素アインスタイニウムを用いた実験(安定の島に向かう超重原子核の核分裂と電子軌道のイオン半径)、(2)電子のスピンを駆使した新しいエネルギー変換仕組み、(3)磁場に負けない超伝導、(4)放射線環境中のセラミックスがもつ自己修復能力
studied by soft X-ray angle-resolved photoemission spectroscopy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
被引用回数：3 パーセンタイル：25.85(Physics, Multidisciplinary)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.
Fe
O
小畠 雅明; 吉井 賢資; 福田 竜生; 川崎 郁斗; 岡根 哲夫; 山上 浩志; 矢板 毅; 針井 一哉; 家田 淳一; 岡安 悟; et al.
JPS Conference Proceedings (Internet), 30, p.011192_1 - 011192_6, 2020/03
スピンゼーベック効果を示す系として注目されているPt/YFeO(YIG)系に対し、放射光を用いた硬X線光電子分光(HAXPES)により表面及び界面の電子状態測定を行った。本系ではスピンゼーベック効果のほかに特異な性質を示すことが報告されている。例えば、外部磁場が存在しない状況でもホール効果を発現する。この起源として、YIG中のFeイオンがPt膜に染み出し、磁性を持つ金属間化合物を生成している可能性が提案されている。そこでHAXPESの分析深さを利用し、界面近傍の鉄イオン等の電子状態を測定した。Ptの厚みが2nm, 5nm, 8nm, 10nmの試料を測定したところ、2nmと5nmの試料において鉄イオンの分析を行うことができた。Fe 1s光電子スペクトルからは、鉄イオンが3+のものと金属的な0価に近い2つの状態が存在することが判明し、上記の可能性を支持する結果が得られた。Pt 4fやO 1sスペクトルなども測定しており、詳しい結果は当日報告する。
studied by 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*
Journal of the Physical Society of Japan, 88(10), p.103701_1 - 103701_5, 2019/10
被引用回数：40 パーセンタイル：88.07(Physics, Multidisciplinary)The electronic structure of the unconventional superconductor 
was studied by resonant photoelectron spectroscopy (RPES) and angle-resolved photoelectron spectroscopy (ARPES) with soft X-ray synchrotron radiation. The partial density of states of were imaged by the 
- RPES and it was found that the state has an itinerant character, but there exists an incoherent peak due to the strong electron correlation effects. Furthermore, an anomalous admixture of the states into the 
bands was observed at a higher binding energy, which cannot be explained by band structure calculations. On the other hand, the band structure of was obtained by ARPES and its overall band structure were mostly explained by band structure calculations. These results suggest that the states of have itinerant but strongly-correlated nature with enhanced hybridization with the states.
ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.
Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07
The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3
contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3 electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3 states have a finite contribution to the density of states at the Fermi energy. These states, presumably consisting of majority-spin 
- hybridized states or minority-spin e states, would be responsible for the ferromagnetic order in this material.
ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.
Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07
被引用回数：16 パーセンタイル：59.40(Materials Science, Multidisciplinary)The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3 contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3 electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3 states have a finite contribution to the density of states at the Fermi energy. These states would be responsible for the ferromagnetic order in this material.
Ge and EuCuSi studied by soft X-ray photoemission spectroscopy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
被引用回数：8 パーセンタイル：35.95(Materials Science, Multidisciplinary)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.
states of uranium compounds revealed by 4-5 resonant photoelectron spectroscopy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
被引用回数：14 パーセンタイル：52.16(Materials Science, Multidisciplinary)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.
Si studied by photoelectron spectroscopy (INVITED)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.
