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Electronic structure of ThPd$$_2$$Al$$_3$$; Impact of the U $$5f$$ states on the electronic structure of UPd$$_2$$Al$$_3$$

藤森 伸一; 竹田 幸治; 山上 浩志; Posp$'i$$v{s}$il, J.*; 山本 悦嗣; 芳賀 芳範

Physical Review B, 105(11), p.115128_1 - 115128_6, 2022/03


The electronic structure of $$mathrm{ThPd_2Al_3}$$, which is isostructural to the heavy fermion superconductor $$mathrm{UPd_2 Al_3}$$, was investigated by photoelectron spectroscopy. The band structure and Fermi surfaces of $$mathrm{ThPd_2Al_3}$$ 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 $$mathrm{ThPd_2Al_3}$$ mainly consists of the $$mathrm{Al}~3p$$ and $$mathrm{Th}~6d$$ states with a minor contribution from the $$mathrm{Pd}~4d$$ states. The comparison of the band structures between $$mathrm{ThPd_2Al_3}$$ and $$mathrm{UPd_2Al_3}$$ argues that the $$mathrm{U}~5f$$ states form Fermi surfaces in $$mathrm{UPd_2Al_3}$$ through hybridization with the $$mathrm{Al}~3p$$ state in the $$mathrm{Al}$$ layer, suggesting that the Fermi surface of $$mathrm{UPd_2Al_3}$$ has a strong three-dimensional nature.


Electronic structure of URu$$_2$$Si$$_2$$ 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 $$mathrm{URu_2Si_2}$$ 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 $$mathrm{U}~5f$$ state were observed near $$E_mathrm{F}$$, formed by the hybridization with the $$mathrm{Ru}~4d$$ states. The energy dispersion of the quasi-particle band is significantly depend on$$k_z$$, 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$$mathrm{URu_2Si_2}$$ is an essential ingredient for modeling its hidden-order transition.


ウランの化学(II); 方法と実践

佐藤 修彰*; 桐島 陽*; 渡邉 雅之; 佐々木 隆之*; 上原 章寛*; 武田 志乃*

ウランの化学(II); 方法と実践, 143 Pages, 2021/03



High temperature gas-cooled reactors

武田 哲明*; 稲垣 嘉之; 相原 純; 青木 健; 藤原 佑輔; 深谷 裕司; 後藤 実; Ho, H. Q.; 飯垣 和彦; 今井 良行; et al.

High Temperature Gas-Cooled Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.5, 464 Pages, 2021/02



Direct observation of the magnetic ordering process in the ferromagnetic semiconductor Ga$$_{1-x}$$Mn$$_{x}$$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:2 パーセンタイル:13.22(Physics, Applied)

In order to understand the mechanism of the ferromagnetism in Ga$$_{1-x}$$Mn$$_{x}$$As ((Ga,Mn)As), we have investigated the magnetic behavior on a microscopic level through systematic temperature ($$T$$) and magnetic-field ($$H$$) dependent soft X-ray magnetic circular dichroism (XMCD) experiments at the Mn $$L_mathrm{2,3}$$ absorption edges. The $$T$$ and $$H$$ 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 ($$T_mathrm{C}$$) values. In particular, the SPM component develops well above $$T_mathrm{C}$$, indicating that local FM regions are formed well above $$T_mathrm{C}$$. 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.


幌延深地層研究計画における地下施設での調査研究段階; (第3段階: 必須の課題2015-2019年度)研究成果報告書

中山 雅; 雑賀 敦; 木村 駿; 望月 陽人; 青柳 和平; 大野 宏和; 宮川 和也; 武田 匡樹; 早野 明; 松岡 稔幸; et al.

JAEA-Research 2019-013, 276 Pages, 2020/03




Manifestation of electron correlation effect in 5$$f$$ states of uranium compounds revealed by 4$$d$$-5$$f$$ 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:7 パーセンタイル:47.66(Materials Science, Multidisciplinary)

In the present study, we have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial $$mathrm{U}~5f$$ density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the $$mathrm{U}$$ 4$$d$$-5$$f$$ resonant photoemission spectroscopy. Obtained $$mathrm{U}~5$$ 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 ($$lesssim 1~mathrm{eV}$$) 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 $$mathrm{U}~5$$ state increases. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard-$$U$$ type mechanism takes an essential role in the $$5f$$ electronic structure of actinide materials.


Electronic structure of URu$$_2$$Si$$_2$$ 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 UPd$$_2$$Al$$_3$$ and URu$$_2$$Si$$_2$$ studied by photoelectron spectroscopy using soft X-rays from SPring-8 BL23SU are presented. For UPd$$_2$$Al$$_3$$, 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 URu$$_2$$Si$$_2$$, and revealed its complete 3D electronic structure in the paramagnetic phase. Their electronic structures are discussed based on these results.


Soft X-ray magnetic circular dichroism study on UGe$$_{2}$$

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

In order to investigate the electronic and magnetic states of UGe$$_{2}$$ element-specifically, we have performed soft X-ray magnetic circular dichroism experiments at the U N$$_{4,5}$$ and Ge L$$_{2,3}$$ 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$$^{5f}$$) in UGe$$_{2}$$ is close to 3. In addition, applying the magneto-optical sum rules analysis to the XMCD spectrum at the U N$$_{4,5}$$ edges, the ratio of orbital magnetic moment to the spin magnetic moment (-M$$_{L}$$/M$$_{S}$$) is estimated to be 2.17. These values of B and -M$$_{L}$$/M$$_{S}$$ are comparable compared with the results of other FM superconductors: URhGe and UCoGe


Element-specific observation of the ferromagnetic ordering process in UCoAl via soft X-ray magnetic circular dichroism

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


 被引用回数:1 パーセンタイル:6.96(Materials Science, Multidisciplinary)

We have performed soft X-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U 4$$d$$-5$$f$$ ($$N_mathrm{4, 5}$$) and Co 2$$p$$-3$$d$$ ($$L_mathrm{2, 3}$$) absorption edges in order to investigate the magnetic properties of the U 5$$f$$ and Co 3$$d$$ electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co 3$$d$$ electrons is unusually large. Through the systematic temperature ($$T$$)- and magnetic field ($$H$$)-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of $$H$$ and $$T$$ (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 $$H_mathrm{M}$$. The value of the $$H_mathrm{M}$$ and its $$T$$-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$$d$$ electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.


Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex, 2; Neutron scattering instruments

中島 健次; 川北 至信; 伊藤 晋一*; 阿部 淳*; 相澤 一也; 青木 裕之; 遠藤 仁*; 藤田 全基*; 舟越 賢一*; Gong, W.*; et al.

Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12



Electronic structure of ThRu$$_2$$Si$$_2$$ studied by angle-resolved photoelectron spectroscopy; Elucidating the contribution of U 5$$f$$ states in URu$$_{2}$$Si$$_{2}$$

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

 被引用回数:8 パーセンタイル:42.32(Materials Science, Multidisciplinary)

The Fermi surface and band structure of $$mathrm{ThRu}_2mathrm{Si}_2$$ have been studied by angle resolved photoelectron spectroscopy (ARPES) with the incident photon energies of $$hnu$$ = 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 $$mathrm{ThRu}_2mathrm{Si}_2$$ with those of $$mathrm{URu}_2mathrm{Si}_2$$ shows that they have considerably different spectral profiles particularly in the energy range of $$E_mathrm{B} = E_mathrm{F}$$ - 1 eV. Some energy bands with their energy dispersions of about 1 eV observed in $$mathrm{URu}_2mathrm{Si}_2$$ are missing in the ARPES spectra of $$mathrm{ThRu}_2mathrm{Si}_2$$ measured along the same high symmetry line of Brillouin zone, suggesting that U 5$$f$$ states form these bands in $$mathrm{URu}_2mathrm{Si}_2$$. The relationship between the ARPES spectra of $$mathrm{URu}_2mathrm{Si}_2$$ and $$mathrm{ThRu}_2mathrm{Si}_2$$ is very different from the case between $$mathrm{CeRu}_2mathrm{Si}_2$$ and $$mathrm{LaRu}_2mathrm{Si}_2$$ where their intrinsic difference is limited only in the very vicinity of the Fermi energy. The present result argues that the U 5$$f$$ electrons in $$mathrm{URu}_2mathrm{Si}_2$$ have strong hybridization with ligand states, and essentially have an itinerant character.


Electronic structures of U$$X_3$$ ($$X$$=Al, Ga, and In) studied by 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, 96(11), p.115126_1 - 115126_10, 2017/09

 被引用回数:6 パーセンタイル:37.68(Materials Science, Multidisciplinary)

The electronic structures of U$$X_3$$ ($$X$$=Al, Ga, and In) were studied by photoelectron spectroscopy to understand the relationship between their electronic structure and magnetic properties. The band structures and Fermi surfaces of UAl$$_3$$ and UGa$$_3$$ 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$$_3$$ and UGa$$_3$$ were explained reasonably well by the calculation, although bands near the Fermi level ($$E_mathrm{F}$$) were renormalized owing to the finite electron correlation effect. The topologies of the Fermi surfaces of UAl$$_3$$ and UGa$$_3$$ 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.



佐藤 稔紀; 笹本 広; 石井 英一; 松岡 稔幸; 早野 明; 宮川 和也; 藤田 朝雄*; 棚井 憲治; 中山 雅; 武田 匡樹; et al.

JAEA-Research 2016-025, 313 Pages, 2017/03




瑞浪超深地層研究所における工学技術に関する検討(平成27年度); 掘削影響の修復・軽減技術の開発(委託研究)

深谷 正明*; 竹田 宣典*; 三浦 律彦*; 石田 知子*; 畑 浩二*; 鵜山 雅夫*; 佐藤 伸*; 大熊 史子*; 早金 沙綾香*; 松井 裕哉; et al.

JAEA-Technology 2016-035, 153 Pages, 2017/02




Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

坂本 祥哉*; 若林 勇希*; 竹田 幸治; 藤森 伸一; 鈴木 博人*; 伴 芳祐*; 山上 浩志; 田中 雅明*; 大矢 忍*; 藤森 淳*

Physical Review B, 95(7), p.075203_1 - 075203_5, 2017/02

 被引用回数:9 パーセンタイル:46.42(Materials Science, Multidisciplinary)

Ge$$_{1-x}$$Fe$$_x$$ (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K and hence is a promising material for spintronic applications compatible with Si technology. We have studied its underlying electronic structure by soft X-ray angle-resolved photoemission spectroscopy measurements and first-principles supercell calculation. We observed finite Fe 3$$d$$ components in the states at the Fermi level ($$Erm_F$$) in a wide region of momentum space, and the $$Erm_F$$ was located $$sim$$0.35 eV above the valence-band maximum of the host Ge. Our calculation indicates that the $$Erm_F$$ is also within the deep acceptor-level impurity band induced by the strong $$p$$-$$d$$($$t_2$$) hybridization. We conclude that the additional minority-spin $$d(e)$$ electron characteristic of the Fe$$^{2+}$$ state is responsible for the short-range ferromagnetic coupling between Fe atoms.


Origin of the large positive magnetoresistance of Ge$$_{1-x}$$Mn$$_{x}$$ granular thin films

若林 勇希*; 秋山 了太*; 竹田 幸治; 堀尾 眞史*; 芝田 悟朗*; 坂本 祥哉*; 伴 芳祐*; 斎藤 祐児; 山上 浩志; 藤森 淳*; et al.

Physical Review B, 95(1), p.014417_1 - 014417_6, 2017/01

 被引用回数:8 パーセンタイル:46.42(Materials Science, Multidisciplinary)

Ge$$_{1_x}$$Mn$$_x$$ (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). The microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of X-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.


Synthesized research report in the second mid-term research phase, Mizunami Underground Research Laboratory Project, Horonobe Underground Research Laboratory Project and Geo-stability Project (Translated document)

濱 克宏; 笹尾 英嗣; 岩月 輝希; 尾上 博則; 佐藤 稔紀; 藤田 朝雄; 笹本 広; 松岡 稔幸; 武田 匡樹; 青柳 和平; et al.

JAEA-Review 2016-014, 274 Pages, 2016/08




Electronic structures of uranium compounds studied by soft X-ray photoelectron spectroscopy

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

 被引用回数:27 パーセンタイル:83.57(Physics, Multidisciplinary)

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$$f$$ 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 $$5f$$ 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$$f^3$$ configuration.


Recent progress of soft X-ray photoelectron spectroscopy studies of uranium compounds

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

 被引用回数:1 パーセンタイル:10.33(Spectroscopy)


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