Electronic structure of ThPdAl; 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

https://doi.org/10.1103/PhysRevB.105.115128

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.

Electronic structure of URuSi 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

https://doi.org/10.1088/2516-1075/abfd20

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.

Direct observation of the magnetic ordering process in the ferromagnetic semiconductor GaMnAs 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

https://doi.org/10.1063/5.0031605

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.

Electronic structure of trivalent compound EuPd 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

https://doi.org/10.7566/JPSJ.89.044704

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.

Electronic structure of UTe 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

https://doi.org/10.7566/JPSJ.88.103701

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.

Electronic structure of the high- 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

https://doi.org/10.1103/PhysRevB.100.035204

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.

Manifestation of electron correlation effect in 5 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

https://doi.org/10.1103/PhysRevB.99.035109

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.

Soft X-ray magnetic circular dichroism study on UGe

竹田 幸治; 岡根 哲夫; 斎藤 祐児; 山上 浩志; 山本 悦嗣; 芳賀 芳範

Progress in Nuclear Science and Technology (Internet), 5, p.171 - 174, 2018/11

https://doi.org/10.15669/pnst.5.171

In order to investigate the electronic and magnetic states of UGe element-specifically, we have performed soft X-ray magnetic circular dichroism experiments at the U N and Ge L absorption edges. We have detected the XMCD signals at both the U and Ge sites and observed clear hysteresis loops in the ferromagnetic (FM) state at T = 5.5 K. From the branching ratio B, it is found that the occupation number of 5f electrons (n) in UGe is close to 3. In addition, applying the magneto-optical sum rules analysis to the XMCD spectrum at the U N edges, the ratio of orbital magnetic moment to the spin magnetic moment (-M/M) is estimated to be 2.17. These values of B and -M/M are comparable compared with the results of other FM superconductors: URhGe and UCoGe

Cation distribution and magnetic properties in ultrathin (NiCo)FeO (x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism

若林 勇希*; 野中 洋亮*; 竹田 幸治; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; 芝田 悟朗*; 田中 新*; 斎藤 祐児; 山上 浩志; et al.

Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10

https://doi.org/10.1103/PhysRevMaterials.2.104416

We study the electronic structure and magnetic properties of epitaxial (NiCo)FeO(111) layers with thicknesses = 1.7 - 5.2 nm grown on AlO(111)/Si(111) structures. We revealed the crystallographic (octahedral or tetrahedral ) sites and the valences of the Fe, Co, and Ni cations using experimental soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra and configuration-interaction cluster-model calculation.

Evidence for momentum-dependent heavy fermionic electronic structures; Soft X-ray ARPES for the superconductor CeNiGe in the normal state

中谷 泰博*; 荒谷 秀和*; 藤原 秀紀*; 森 健雄*; 鶴田 篤史*; 橘 祥一*; 山口 貴司*; 木須 孝幸*; 山崎 篤志*; 保井 晃*; et al.

Physical Review B, 97(11), p.115160_1 - 115160_7, 2018/03

AA2018-0003.pdf:1.65MB

https://doi.org/10.1103/PhysRevB.97.115160

We present clear experimental evidence for the momentum-dependent heavy fermionic electronic structures of the 4-based strongly correlated system CeNiGe by soft X-ray angle-resolved photoemission spectroscopy. A comparison between the experimental three-dimensional quasiparticle dispersion of LaNiGe and CeNiGe has revealed that heavy fermionic electronic structures are seen in the region surrounding at a specific momentum. Furthermore, the wave vectors between the observed "heavy spots" are consistent with a result of neutron scattering reflecting magnetic correlations, which could be a trigger of the superconductivity in CeNiGe.