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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:0 パーセンタイル:0(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.
出田 真一郎*; Johnston, S.*; 吉田 鉄平*; 田中 清尚*; 森 道康; 安齋 太陽*; 井野 明洋*; 有田 将司*; 生天目 博文*; 谷口 雅樹*; et al.
Physical Review Letters, 127(21), p.217004_1 - 217004_6, 2021/11
被引用回数:0 パーセンタイル:0(Physics, Multidisciplinary)Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO layers in the triple-layer cuprate high-temperature superconductor Bi
Sr
Ca
Cu
O
is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anti-crossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the
-wave superconducting gap of both BQP bands smoothly develops with momentum without abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off-nodal to the anti-nodal region, which is explained by the momentum-dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs, as well as the combination of phonon modes of the triple CuO
layers and spin fluctuations are discussed.
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(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 SrNi
P
. The heavy-fermion bands in EuNi
P
are thus considered to be formed through the hybridization between the dispersive valence bands, which resemble those for SrNi
P
, and the Eu
components located at the very vicinity of the Fermi level.
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.
Shick, A. B.*; 藤森 伸一; Pickett, W. E.*
Physical Review B, 103(12), p.125136_1 - 125136_12, 2021/03
被引用回数:9 パーセンタイル:84.02(Materials Science, Multidisciplinary)Correlated band theory implemented as a combination of density functional theory with exact diagonalization [DFT+(ED)] of the Anderson impurity term with Coulomb repulsion U in the open 14-orbital 5f shell is applied to UTe
. The small gap for
=0, evidence of the half-filled
subshell of 5
uranium, is converted for
= 3 eV to a flat band semimetal with small heavy-carrier Fermi surfaces that will make properties sensitive to pressure, magnetic field, and off stoichiometry, as observed experimentally. Two means of identification from the Green's function give a mass enhancement of the order of 12 for already heavy (flat) bands, consistent with the common heavy-fermion characterization of UTe
. The predicted Kondo temperature around 100 K matches the experimental values from resistivity. The electric field gradients for the two Te sites are calculated by DFT+
(ED) to differ by a factor of seven, indicating a strong site distinction, while the anisotropy factor
= 0.18 is similar for all three sites. The calculated uranium moment
of 3.5
is roughly consistent with the published experimental Curie-Weiss values of 2.8
and 3.3
, and the calculated separate spin and orbital moments are remarkably similar to Hund's rule values for an
ion. The
=3 eV spectral density is compared with angle-integrated and angle-resolved photoemission spectra, with agreement that there is strong 5f character at, and for several hundred meV below, the Fermi energy. Our results support the picture that the underlying ground state of UTe
is that of a half-filled
subshell with two half-filled
orbitals forming a narrow gap by hybridization, then driven to a conducting state by configuration mixing (spin-charge fluctuations). UTe
displays similarities to UPt
with its 5f dominated Fermi surfaces rather than a strongly localized Kondo lattice system.
Kataoka, Noriyuki*; Tanaka, Masashi*; Hosoda, Wataru*; Taniguchi, Takumi*; 藤森 伸一; Wakita, Takanori*; Muraoka, Yuji*; Yokoya, Takashi*
Journal of Physics; Condensed Matter, 33(3), p.035501_1 - 035501_6, 2021/01
被引用回数:3 パーセンタイル:45.08(Physics, Condensed Matter)We have performed soft X-ray spectroscopy in order to study thephotoirradiation time dependence of the valence band structure and chemicalstates of layered transition metal nitride chloride TiNCl. Under the soft X-ray irradiation, the intensities of the states near the Fermi level ()and the Ti
component increased, while the Cl 2
intensity decreased. Ti2
-3
resonance photoemission spectroscopy confirmed a distinctive Fermiedge with Ti 3
character. These results indicate the photo-inducedmetallization originates from deintercalation due to Cl desorption, and thusprovide a new carrier doping method that controls the conducting propertiesof TiNCl.
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:10 パーセンタイル:87.43(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.
Usachov, D. Yu*; Tarasov, A. V.*; Schulz, S.*; Bokai, K. A.*; Tupitsyn, I. I.*; Poelchen, G.*; Seiro, S.*; Caroca-Canales, N.*; Kliemt, K.*; Mende, M.*; et al.
Physical Review B, 102(20), p.205102_1 - 205102_11, 2020/11
被引用回数:7 パーセンタイル:57.37(Materials Science, Multidisciplinary)Using photoelectron diffraction (PED) and magnetic dichroism measurements, we explore the electronic and magnetic properties of the near-surface region of the valence-fluctuating material EuIrSi
. We present and discuss the methodology for modeling of the 4
photoemission spectra, PED patterns and magnetic dichroism for rare-earth-based materials. For the Eu-terminated surface we found that the topmost Eu layer is divalent and exhibits a ferromagnetic order below 10 K. The valency of the next Eu layer, that is the 5th atomic layer, is about 2.8 at low temperature that is close to the valency in the bulk. The properties of the Si-terminated surface are drastically different. The first subsurface Eu layer (4th atomic layer below the surface) behaves divalently and orders ferromagnetically at much higher temperature. Experimental data indicate, however, that there is an admixture of trivalent Eu in this layer, resulting in its valency of about 2.1. The next deeper lying Eu layer (8th atomic layer below the surface) behaves mixed-valently, but the estimated valency of 2.4 is notably lower than the value in the bulk. The obtained results create a background for further studies of exotic surface properties of 4
-based materials, and allow to derive information related to valency and magnetism of individual rare-earth layers in a rather extended area near the surface.
明午 伸一郎; 大井 元貴; 藤森 寛*
Physical Review Accelerators and Beams (Internet), 23(6), p.062802_1 - 062802_24, 2020/06
被引用回数:2 パーセンタイル:34.22(Physics, Nuclear)加速器駆動の核変換システム(ADS)や核破砕中性子源に用いられる陽子加速器のビーム出力増強につれ、ビーム窓や標的の損傷は深刻な問題となり、損傷緩和のためにビーム電流密度の均一化が重要となる。密度均一化のため比較的よく用いられるラスター磁石には、故障時のビーム集束の重大な問題がある。一方、非線形光学を用いたビーム平坦化にはビーム拡大の問題があることが指摘され、これまで非線形効果導入の八極磁石におけるビームの角度の広がりを無視したフィラメント近似模型による検討が行われた。フィラメント近似模型では、非線形収斂作用を適切に評価できないため、本研究では一般化した非線形モデルの適用により非線形ビーム光学における収斂および発散作用を詳細に検討した。正規化した八極強度と位相進行
における
の2つのパラメータ導入により、非線形効果を特定な条件によらず一般化できることを明確にした。ビームのピーク密度低減と損失最小化という拮抗する問題の解決には、
1および
3とすることにより解決できることが判明した。J-PARCの陽子ビーム輸送系(3NBT)に本検討結果を適用し、核破砕中性子源の水銀標的入口のビーム形状の比較検討した結果、モデル計算によるビーム分布は実験データとよい一致を示し、線形光学においてピーク電流密度を約50%にできることを示した。
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:39.72(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.
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:21 パーセンタイル:85.14(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.
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:7 パーセンタイル:45.76(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 EuCu
Si
grown by the Bridgman method to investigate their electronic structures. The AIPES results showed that the Eu ions in EuCu
Ge
and EuCu
Si
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 EuCu
Ge
and EuCu
Si
were studied by ARPES measurements. We found that the band structures near the Fermi level and Fermi surfaces of EuCu
Ge
and EuCu
Si
are very different from each other and are well reproduced by the band structure calculations based on density-functional theory for SrCu
Ge
and YCu
Si
. 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 EuCu
Ge
and EuCu
Si
.
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.
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:12 パーセンタイル:64.92(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.
Gttler, M.*; Generalov, A.*; 藤森 伸一; Kummer, K.*; Chikina, A.*; Seiro, S.*; Danzenb
cher, S.*; Koroteev, Yu. M.*; Chulkov, E. V.*; Radovic, M.*; et al.
Nature Communications (Internet), 10, p.796_1 - 796_7, 2019/02
被引用回数:9 パーセンタイル:65.83(Multidisciplinary Sciences)Application of the Luttinger Theorem (LT) to the canonical heavy-fermion Kondo Lattice (KL) material YbRhSi
suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local moment anti-ferromagnet (AFM) EuRh
Si
in its PM regime. This leads to the tempting opportunity to explore a new experimental realization of the LT in general and how the large FS may change upon the AFM transition below 70 mK in YbRh
Si
in particular. A detailed knowledge of the FS reconstruction might be essential to disclose the properties of this phase, which is a precursor of quantum criticality and superconductivity. Using angle-resolved photoemission spectroscopy (ARPES), we observe a large FS for PM EuRh
Si
essentially the same as the one seen in YbRh
Si
in the KL state at a temperature of 1 K. Across the EuRh
Si
AFM transition we found an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Doughnut and Jungle gym Fermi-surface sheets. Our results on EuRh
Si
indicate that the formation of the AFM state in YbRh
Si
is very likely also connected with large changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system.
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:45.76(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.
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 URu
Si
studied by photoelectron spectroscopy using soft X-rays from SPring-8 BL23SU are presented. For UPd
Al
, 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
Si
, and revealed its complete 3D electronic structure in the paramagnetic phase. Their electronic structures are discussed based on these results.
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:43.28(Materials Science, Multidisciplinary)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
被引用回数:6 パーセンタイル:34.81(Materials Science, Multidisciplinary)The electronic structures of U (
=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
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.
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:46.79(Materials Science, Multidisciplinary)GeFe
(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
components in the states at the Fermi level (
) in a wide region of momentum space, and the
was located
0.35 eV above the valence-band maximum of the host Ge. Our calculation indicates that the
is also within the deep acceptor-level impurity band induced by the strong
-
(
) hybridization. We conclude that the additional minority-spin
electron characteristic of the Fe
state is responsible for the short-range ferromagnetic coupling between Fe atoms.