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Takafumi Sato - One of the best experts on this subject based on the ideXlab platform.
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Superstructure-dependent electronic states in CaAlSi superconductors studied by Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2015Co-Authors: Takafumi Sato, Katsuaki Sugawara, Seigo Souma, Jun Akimitsu, Y. X. Xiao, Kosuke Nakayama, S. Kuroiwa, Takashi TakahashiAbstract:We have performed high-resolution Angle-Resolved Photoemission Spectroscopy on layered polymorph series of $1H\ensuremath{-}, 5H\ensuremath{-}$, and $6H\ensuremath{-}\mathrm{CaAlSi}$, which exhibit superconductivity below 6.5, 5.7, and 7.7 K, respectively. While the overall band structure in the valence-band region is similar among these compounds, the volume of the Fermi surface at the $M$ point and the magnitude of the superconducting gap are markedly different from each other. Implications of such variation in the electronic structure due to the superstructure along the $c$ axis are discussed in relation to the physical properties of CaAlSi.
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Fe-based superconductors: an Angle-Resolved Photoemission Spectroscopy perspective
Reports on Progress in Physics, 2011Co-Authors: Pierre Richard, Takafumi Sato, Takashi Takahashi, K. Nakayama, Hong DingAbstract:Angle-Resolved Photoemission Spectroscopy allows direct visualization and experimental determination of the electronic structure of crystals in the momentum space, including the precise characterization of the Fermi surface and the superconducting order parameter. It is thus particularly suited for investigating multi-band systems such as the Fe-based superconductors. In this review, we cover several aspects of these recently discovered materials that have been addressed by this technique, with a special emphasis on their superconducting gap and their Fermi surface topology. We provide sufficient experimental evidence to support the reliability and the consistency of the Angle-Resolved Photoemission Spectroscopy measurements over a wide range of material compositions.
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Angle-Resolved Photoemission Spectroscopy of Graphene, Graphite, and Related Compounds
Comprehensive Semiconductor Science and Technology, 2011Co-Authors: Takafumi Sato, Takashi TakahashiAbstract:High-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) studies on carbon-based materials, such as graphene, graphite, and graphite intercalation compounds (GICs), are presented. We briefly review the basic principle of ARPES technique as well as the recent development of experimental apparatus, and then focus on the electronic structure in the vicinity of the Fermi level responsible for novel physical properties. We discuss the energy band structure and the Fermi surface of graphene and graphite in terms of the many-body interaction, the edge-localized states, and the Dirac-fermion-like behavior. We also explain the first direct ARPES observation of the interlayer band and the superconducting gap in a high-Tc GIC, C6Ca.
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Three-dimensional band structure of highly metallic Na0.8WO3 by Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2009Co-Authors: Satyabrata Raj, Takafumi Sato, Takashi Takahashi, Anirban Chakraborty, Debraj Choudhury, Priya Mahadevan, Jun Fujii, Ivana Vobornik, D. D. SarmaAbstract:Three-dimensional electronic structure of highly metallic sodium tungsten bronze, Na0.8WO3, is investigated by high-resolution Angle-Resolved Photoemission Spectroscopy. The experimentally determined valence-band structure along the momentum directions both parallel and perpendicular to the surface has been compared with the results of ab initio band-structure calculation. The Angle-Resolved Photoemission Spectroscopy spectra for different photon energies reveal that possibly the oxygen vacancies in the system are responsible for the evolution of density of states at the top of Gamma point in experimental valence band. The band dispersion around Gamma(X) point leading to an electronlike Fermi surface is well predicted by the band calculation. As we move from bulk-sensitive to more-surface-sensitive photon energy, we found emergence of Fermi surfaces at X(M) and M(R) points similar to the one at Gamma(X) point, suggesting the reconstruction of surface due to rotation/deformation of WO6 octahedra.
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Fermi Surface and Band Dispersions of MxCoO2 (M: Na, K, and Rb) Studied by Angle-Resolved Photoemission Spectroscopy
Journal of the Physical Society of Japan, 2007Co-Authors: Toshiyuki Arakane, Takafumi Sato, Takashi Takahashi, Hong Ding, Takenori Fujii, Atsushi AsamitsuAbstract:We have performed Angle-Resolved Photoemission Spectroscopy (ARPES) on MxCoO2 (M: Na, K, and Rb) with both soft X-ray and ultraviolet light to clarify the electronic structure intrinsic to the bulk CoO2 plane. We observed a large holelike a(1g) Fermi surf
Takashi Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Superstructure-dependent electronic states in CaAlSi superconductors studied by Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2015Co-Authors: Takafumi Sato, Katsuaki Sugawara, Seigo Souma, Jun Akimitsu, Y. X. Xiao, Kosuke Nakayama, S. Kuroiwa, Takashi TakahashiAbstract:We have performed high-resolution Angle-Resolved Photoemission Spectroscopy on layered polymorph series of $1H\ensuremath{-}, 5H\ensuremath{-}$, and $6H\ensuremath{-}\mathrm{CaAlSi}$, which exhibit superconductivity below 6.5, 5.7, and 7.7 K, respectively. While the overall band structure in the valence-band region is similar among these compounds, the volume of the Fermi surface at the $M$ point and the magnitude of the superconducting gap are markedly different from each other. Implications of such variation in the electronic structure due to the superstructure along the $c$ axis are discussed in relation to the physical properties of CaAlSi.
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Fe-based superconductors: an Angle-Resolved Photoemission Spectroscopy perspective
Reports on Progress in Physics, 2011Co-Authors: Pierre Richard, Takafumi Sato, Takashi Takahashi, K. Nakayama, Hong DingAbstract:Angle-Resolved Photoemission Spectroscopy allows direct visualization and experimental determination of the electronic structure of crystals in the momentum space, including the precise characterization of the Fermi surface and the superconducting order parameter. It is thus particularly suited for investigating multi-band systems such as the Fe-based superconductors. In this review, we cover several aspects of these recently discovered materials that have been addressed by this technique, with a special emphasis on their superconducting gap and their Fermi surface topology. We provide sufficient experimental evidence to support the reliability and the consistency of the Angle-Resolved Photoemission Spectroscopy measurements over a wide range of material compositions.
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Angle-Resolved Photoemission Spectroscopy of Graphene, Graphite, and Related Compounds
Comprehensive Semiconductor Science and Technology, 2011Co-Authors: Takafumi Sato, Takashi TakahashiAbstract:High-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) studies on carbon-based materials, such as graphene, graphite, and graphite intercalation compounds (GICs), are presented. We briefly review the basic principle of ARPES technique as well as the recent development of experimental apparatus, and then focus on the electronic structure in the vicinity of the Fermi level responsible for novel physical properties. We discuss the energy band structure and the Fermi surface of graphene and graphite in terms of the many-body interaction, the edge-localized states, and the Dirac-fermion-like behavior. We also explain the first direct ARPES observation of the interlayer band and the superconducting gap in a high-Tc GIC, C6Ca.
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Three-dimensional band structure of highly metallic Na0.8WO3 by Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2009Co-Authors: Satyabrata Raj, Takafumi Sato, Takashi Takahashi, Anirban Chakraborty, Debraj Choudhury, Priya Mahadevan, Jun Fujii, Ivana Vobornik, D. D. SarmaAbstract:Three-dimensional electronic structure of highly metallic sodium tungsten bronze, Na0.8WO3, is investigated by high-resolution Angle-Resolved Photoemission Spectroscopy. The experimentally determined valence-band structure along the momentum directions both parallel and perpendicular to the surface has been compared with the results of ab initio band-structure calculation. The Angle-Resolved Photoemission Spectroscopy spectra for different photon energies reveal that possibly the oxygen vacancies in the system are responsible for the evolution of density of states at the top of Gamma point in experimental valence band. The band dispersion around Gamma(X) point leading to an electronlike Fermi surface is well predicted by the band calculation. As we move from bulk-sensitive to more-surface-sensitive photon energy, we found emergence of Fermi surfaces at X(M) and M(R) points similar to the one at Gamma(X) point, suggesting the reconstruction of surface due to rotation/deformation of WO6 octahedra.
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Fermi Surface and Band Dispersions of MxCoO2 (M: Na, K, and Rb) Studied by Angle-Resolved Photoemission Spectroscopy
Journal of the Physical Society of Japan, 2007Co-Authors: Toshiyuki Arakane, Takafumi Sato, Takashi Takahashi, Hong Ding, Takenori Fujii, Atsushi AsamitsuAbstract:We have performed Angle-Resolved Photoemission Spectroscopy (ARPES) on MxCoO2 (M: Na, K, and Rb) with both soft X-ray and ultraviolet light to clarify the electronic structure intrinsic to the bulk CoO2 plane. We observed a large holelike a(1g) Fermi surf
Seigo Souma - One of the best experts on this subject based on the ideXlab platform.
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Superstructure-dependent electronic states in CaAlSi superconductors studied by Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2015Co-Authors: Takafumi Sato, Katsuaki Sugawara, Seigo Souma, Jun Akimitsu, Y. X. Xiao, Kosuke Nakayama, S. Kuroiwa, Takashi TakahashiAbstract:We have performed high-resolution Angle-Resolved Photoemission Spectroscopy on layered polymorph series of $1H\ensuremath{-}, 5H\ensuremath{-}$, and $6H\ensuremath{-}\mathrm{CaAlSi}$, which exhibit superconductivity below 6.5, 5.7, and 7.7 K, respectively. While the overall band structure in the valence-band region is similar among these compounds, the volume of the Fermi surface at the $M$ point and the magnitude of the superconducting gap are markedly different from each other. Implications of such variation in the electronic structure due to the superstructure along the $c$ axis are discussed in relation to the physical properties of CaAlSi.
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Electronic structure of LaAgSb2 and CeAgSb2 studied by high-resolution Angle-Resolved Photoemission Spectroscopy
Journal of Magnetism and Magnetic Materials, 2007Co-Authors: Toshiyuki Arakane, Seigo Souma, Takafumi Sato, Takashi Takahashi, Y. Watanabe, Yoshihiko InadaAbstract:Abstract We performed high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) on quasi-two-dimensional rare-earth intermetallic compounds LaAgSb 2 and CeAgSb 2 . In CeAgSb 2 , we found highly dispersive bands in the vicinity of the Fermi level, showing a hole-like dispersion centered at the Γ(Z) point in the Brillouin zone. These bands produce small hole pockets at the zone center, in good agreement with the band calculation of LaAgSb 2 .
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Anomalous electronic states in graphite studied by Angle-Resolved Photoemission Spectroscopy
Science and Technology of Advanced Materials, 2006Co-Authors: Katsuaki Sugawara, Seigo Souma, Takafumi Sato, Takashi Takahashi, Hiroshi SuematsuAbstract:We report high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) on high quality single crystal of graphite (kish graphite) to elucidate the origin of anomalous physical properties of carbon-based materials. We found an almost flat band in the vicinity of the Fermi level around the K(H) point which is not predicted by the bulk band calculation. We discuss the origin of this anomalous structure in relation to the edge-localized state on the step edges of cleaved surface.
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Electronic band structure of AlB2 studied by Angle-Resolved Photoemission Spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2005Co-Authors: Seigo Souma, Takafumi Sato, Takashi Takahashi, Noriaki Kimura, H. AokiAbstract:Abstract We have performed UV and X-ray Angle-Resolved Photoemission Spectroscopy (ARPES) on AlB 2 which is a non-superconducting reference of MgB 2 . We found that the \sigma -band is totally occupied in AlB 2 in contrast to the partially occupied \sigma -band in MgB 2 , which suggests that the \sigma -band on the Fermi level is essential for the superconductivity. We also found an electron pocket centered at the Γ (A) point in the UVARPES spectrum as in MgB 2 , while it is absent in the X-ray ARPES spectra. This indicates that the electron pocket is of surface origin.
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Direct observation of superconducting gaps in MgB2 by Angle-Resolved Photoemission Spectroscopy
Physica C-superconductivity and Its Applications, 2004Co-Authors: Seigo Souma, Takafumi Sato, Takashi Takahashi, Hong Ding, Yo Machida, S. C. Wang, Hideki Matsui, Adam Kaminski, J. C. Campuzano, Satoshi SasakiAbstract:High-resolution Angle-Resolved Photoemission Spectroscopy has been carried out to clarify the anomalous superconductivity of MgB2. We observed three bands crossing the Fermi level, which are ascribed to B2p-sigma, pi and surface bands. We have succeeded f
Yoshichika Ōnuki - One of the best experts on this subject based on the ideXlab platform.
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Electronic Structure of Trivalent Compound EuPd3 Studied by Soft X-ray Angle-Resolved Photoemission Spectroscopy
Journal of the Physical Society of Japan, 2020Co-Authors: Ikuto Kawasaki, M. Kobata, Shin-ichi Fujimori, Yukiharu Takeda, Hiroshi Yamagami, Ai Nakamura, Wataru Iha, Masato Hedo, Takao Nakama, Yoshichika ŌnukiAbstract:EuPd3 is a rare Eu-based compound, whose Eu ions are in a trivalent state. The electronic structure of EuPd3 was investigated by Angle-Resolved Photoemission Spectroscopy (ARPES) using soft x rays....
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Itinerant U 5f Nature in Antiferromagnet U(Ru0.97Rh0.03)2Si2: Soft X-ray Angle-Resolved Photoemission Spectroscopy
Journal of the Physical Society of Japan, 2011Co-Authors: Ikuto Kawasaki, Yoshinori Haga, E. Yamamoto, Shin-ichi Fujimori, Hiroshi Yamagami, Tetsuo Okane, Akira Yasui, Yuji Saitoh, Yoshichika ŌnukiAbstract:We have carried out soft X-ray Angle-Resolved Photoemission Spectroscopy experiments on U(Ru 0.97 Rh 0.03 ) 2 Si 2 , which shows antiferromagnetic (AFM) ordering at low temperatures. We have reveal...
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Band structure ofUPd3studied by ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2002Co-Authors: Takahiro Ito, Seigo Souma, Hiroshi Kumigashira, Yoshinori Haga, Yoshihumi Tokiwa, T. Takahashi, Yoshichika ŌnukiAbstract:We have performed ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy on UPd 3 to study the band structure near the Fermi level (E F ) and the Fermi surface. We found three Fermi surfaces (FS's): two hole pockets with a dominant Pd 4d character at the Γ (A) point and an electron pocket with a U 6d nature at the K (H) point. These FS's are qualitatively well reproduced in the band structure calculation based on the localized U-5f-electron model, while remarkable quantitative discrepancies are observed near E F . The U 5f states are located 0.4-1.0 eV below E F and do not contribute to the Fermi surface. These results indicate the strongly localized nature of U 5f electrons in UPd 3 .
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Ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy of UPd3
Physica B-condensed Matter, 2001Co-Authors: Takahiro Ito, Seigo Souma, Takashi Takahashi, Hiroshi Kumigashira, Yoshinori Haga, Yoshihumi Tokiwa, Yoshichika ŌnukiAbstract:Abstract We have studied the electronic band structure and the Fermi surface of UPd 3 with ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy. It was found that non-dispersive U 5f “bands” are located far below the Fermi level and the main body of valence band consists of Pd 4d-U 6d hybridized dispersive bands in qualitatively good agreement with the band-structure calculation based on the localized U 5f model. We found two hole-like Fermi surfaces with a dominant Pd 4d character at Γ ( A ) point and an electron-like one with a U 6d nature at K( H ) point.
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Angle-Resolved Photoemission Spectroscopy of UPt3
Physica B-condensed Matter, 1999Co-Authors: Takahiro Ito, Takashi Takahashi, Hiroshi Kumigashira, Hyeong-do Kim, Noriaki Kimura, Yoshinori Haga, E. Yamamoto, Yoshichika Ōnuki, Hisatomo HarimaAbstract:Abstract We have performed Angle-Resolved Photoemission Spectroscopy on UPt3. The experimental result has been compared with the band structure calculation including the U 5f states. The overall feature of Pt 5d bands shows a good agreement between experiment and calculation, while the experimental U 5f band is much narrower, indicative of the strong renormalization.
Takahiro Ito - One of the best experts on this subject based on the ideXlab platform.
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Orbital-dependent electron correlation in LiFeAs revealed by Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2016Co-Authors: Tetsuya Hajiri, Takahiro Ito, Yong Seung Kwon, Masaharu Matsunami, B. H. Min, Kazuhiko Kuroki, S. KimuraAbstract:We report on the electronic structure of the 111-type iron pnictide superconductor LiFeAs as a function of temperature using Angle-Resolved Photoemission Spectroscopy. Below approximately 50 K, both the ${d}_{yz}$ hole band at the $Z$ point and the ${d}_{xz/yz}$ electron band at the $A$ point shift to a higher binding energy side. However, at the high-symmetry points $Z,\phantom{\rule{0.16em}{0ex}}A,\phantom{\rule{0.16em}{0ex}}\mathrm{\ensuremath{\Gamma}}$, and $M$, the remaining bands are almost independent of temperature. One of the possible scenarios for these observations is that a strong, three-dimensional orbital-dependent correlation exists in the normal state of LiFeAs in relation to short-range spin fluctuations.
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Band structure ofUPd3studied by ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2002Co-Authors: Takahiro Ito, Seigo Souma, Hiroshi Kumigashira, Yoshinori Haga, Yoshihumi Tokiwa, T. Takahashi, Yoshichika ŌnukiAbstract:We have performed ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy on UPd 3 to study the band structure near the Fermi level (E F ) and the Fermi surface. We found three Fermi surfaces (FS's): two hole pockets with a dominant Pd 4d character at the Γ (A) point and an electron pocket with a U 6d nature at the K (H) point. These FS's are qualitatively well reproduced in the band structure calculation based on the localized U-5f-electron model, while remarkable quantitative discrepancies are observed near E F . The U 5f states are located 0.4-1.0 eV below E F and do not contribute to the Fermi surface. These results indicate the strongly localized nature of U 5f electrons in UPd 3 .
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Electronic structure of black SmS. II. Angle-Resolved Photoemission Spectroscopy
Physical Review B, 2002Co-Authors: Takahiro Ito, Takashi Takahashi, Hiroshi Kumigashira, Ashish Chainani, Noriaki K. SatoAbstract:We have studied the electronic band structure of semiconducting black SmS with high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES). The valence band consists of two well-separated groups of bands: almost nondispersive bands near E F and highly dispersive bands at higher binding energy. The former is ascribed to the Sm 2 (4f 6 →4f 5 ) multiplet and the latter to mainly the S 3p states. We found a small but distinct energy dispersion in the Sm 4f-derived bands near E F . This indicates a strong hybridization between the "localized" Sm 4f electrons and the "itinerant" conduction electrons, leading to the "delocalized" Sm 4f states in mixed-valent SmS. We have compared the present ARPES results with a recent periodic Anderson model calculation [C. Lehner et al., Phys. Rev. B 58, 6807 (1998)].
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Ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy of UPd3
Physica B-condensed Matter, 2001Co-Authors: Takahiro Ito, Seigo Souma, Takashi Takahashi, Hiroshi Kumigashira, Yoshinori Haga, Yoshihumi Tokiwa, Yoshichika ŌnukiAbstract:Abstract We have studied the electronic band structure and the Fermi surface of UPd 3 with ultrahigh-resolution Angle-Resolved Photoemission Spectroscopy. It was found that non-dispersive U 5f “bands” are located far below the Fermi level and the main body of valence band consists of Pd 4d-U 6d hybridized dispersive bands in qualitatively good agreement with the band-structure calculation based on the localized U 5f model. We found two hole-like Fermi surfaces with a dominant Pd 4d character at Γ ( A ) point and an electron-like one with a U 6d nature at K( H ) point.
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Angle-Resolved Photoemission Spectroscopy of UPt3
Physica B-condensed Matter, 1999Co-Authors: Takahiro Ito, Takashi Takahashi, Hiroshi Kumigashira, Hyeong-do Kim, Noriaki Kimura, Yoshinori Haga, E. Yamamoto, Yoshichika Ōnuki, Hisatomo HarimaAbstract:Abstract We have performed Angle-Resolved Photoemission Spectroscopy on UPt3. The experimental result has been compared with the band structure calculation including the U 5f states. The overall feature of Pt 5d bands shows a good agreement between experiment and calculation, while the experimental U 5f band is much narrower, indicative of the strong renormalization.