Nature Portfolio Acta Medica Okayama 2045-2322 15 1 2025 Local-structure insight into the improved superconducting properties of Pb-substituted La(O, F)BiS2: a photoelectron holography study 8366 EN Yajun Li Graduate School of Natural Science and Technology, Okayama University Yusuke Hashimoto Nara Institute of Science and Technology (NAIST) Noriyuki Kataoka Graduate School of Natural Science and Technology, Okayama University Zexu Sun Nara Institute of Science and Technology (NAIST) Sota Kawamura Nara Institute of Science and Technology (NAIST) Hiroto Tomita Nara Institute of Science and Technology (NAIST) Taro Setoguchi Graduate School of Natural Science and Technology, Okayama University Soichiro Takeuchi Nara Institute of Science and Technology (NAIST) Shunjo Koga Nara Institute of Science and Technology (NAIST) Kohei Yamagami Japan Synchrotron Radiation Research Institute (JASRI) Yoshinori Kotani Japan Synchrotron Radiation Research Institute (JASRI) Satoshi Demura Department of Physics, College of Science and Technology(CST), Nihon University Kanako Noguchi Tokyo University of Science Hideaki Sakata Tokyo University of Science Tomohiro Matsushita Nara Institute of Science and Technology (NAIST) Takanori Wakita Graduate School of Natural Science and Technology, Okayama University Yuji Muraoka Graduate School of Natural Science and Technology, Okayama University Takayoshi Yokoya Graduate School of Natural Science and Technology, Okayama University Pb-substituted La(O, F)BiS2 (Pb-LaOFBiS2) exhibits improved superconducting properties and a resistivity anomaly around 100 K that is attributed to a structural transition. We have performed temperature(T)-dependent photoelectron holography (PEH) to study dopant incorporation sites and the local structure change across the anomaly. The PEH study of Pb-LaOFBiS2 provided evidence for the dominant incorporation sites of Pb and F: Pb atoms are incorporated into the Bi sites and F atoms are incorporated into the O site. No remarkable difference in the local structures around Pb and Bi atoms was observed. Across the temperature of the resistivity anomaly (T*), photoelectron holograms of Bi 4f changed. Comparisons of holograms with those of non-substituted LaOFBiS2 sample, as well as simulated holograms, suggested that (1), above T*, the tetragonal structure of Pb-LaOFBiS2 is different from the tetragonal structure of LaOFBiS2 and (2), below T*, the tetragonal structure still remains in Pb-LaOFBiS2. We discuss a possible origin of the difference in the structure above T* and the implication of the result below T*, which are necessary ingredients to understand the physical properties of Pb-LaOFBiS2. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0925-9635 143 2024 First-principles molecular dynamics simulations for the properties of boron-doped tetrahedral amorphous carbon 110894 EN Qiang Yue Graduate School of Natural Science and Technology, Okayama University Takayoshi Yokoya Research Institute for Interdisciplinary Science, Okayama University Yuji Muraoka Research Institute for Interdisciplinary Science, Okayama University Based on first-principles molecular dynamics (FPMD) simulations combined with a liquid quenching method, we study the effects of boron doping at 0 %, 2 %, 4 %, 6 % on the properties of tetrahedral amorphous carbon (ta-C) with an initial density of 3.0 g/cm3. The results of bond structures and internal stress show the promotion of graphitization with increase in the concentration of boron doping. In addition, simulation of electronic states reveals that the Fermi level shifts to valence band and the intensity of density of electronic states near Fermi level increases with the boron concentration increasing. A covalent bond formation between carbon and boron atoms is also shown by analyzing projected densities of electronic states (PDOS) and electron density distribution. The results of electronic state and bond formation strongly indicate that the boron-doped ta-C is like a p-type semiconductor. The present simulation results provide useful information for deeper understanding on the physical properties of boron-doped ta-C. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0925-9635 140 2023 Molecular dynamics simulation of deposition of amorphous carbon films on sapphire surfaces 110514 EN Qiang Yue Graduate School of Natural Science and Technology, Okayama University Takayoshi Yokoya Research Institute for Interdisciplinary Science, Okayama University Yuji Muraoka Research Institute for Interdisciplinary Science, Okayama University The growth of amorphous carbon films on a sapphire surface was investigated using classical molecular dynamics simulation. The kinetic energy of carbon particles was set as 10 eV and ReaxFF potential was used to express the interaction between different kinds of particles. The results of the temperature distribution in both deposition time and deposition space are reported. Simulation results reveal that the grown amorphous carbon film consists of four regions, namely interlayer, low density, stable growth, and surface regions. In the interlayer region, the interlayer between substrate and pure carbon film is formed. In the low density region, a pure carbon film is grown while the film density decreases initially and then increases. In the stable growth region, the film density remains almost constant. The film density decreases rapidly in the surface region. The radial distribution function (RDF) analysis suggests that a structure similar to that of diamond exists in the stable growth region of the film. The lower film density in the low density and surface regions was interpreted to indicate the existence of abundant sp1 chain structures, which is supported by the depth profile of the sp fractions. The present results are in good agreement with previous experimental and simulation results and demonstrate the suitability of the ReaxFF potential in the simulation of amorphous carbon growth on sapphire substrate. Our study provides a good starting point for the simulation study of amorphous carbon films on sapphire substrates. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0021-4922 62 12 2023 Photoelectron holographic evidence for the incorporation site of Se and suppressed atomic displacement of the conducting layer of La(O,F)BiSSe 125001 EN YaJun Li Engineering Research Center of Integrated Circuit Packaging and Testing, Ministry of Education, Tianshui Normal University ZeXu Sun Nara Institute of Science and Technology (NAIST) Noriyuki Kataoka Graduate School of Natural Science and Technology, Okayama University Taro Setoguchi Graduate School of Natural Science and Technology, Okayama University Yusuke Hashimoto Nara Institute of Science and Technology (NAIST) Soichiro Takeuchi Nara Institute of Science and Technology (NAIST) Shunjo Koga Nara Institute of Science and Technology (NAIST) Kazuhisa Hoshi Department of Physics, Tokyo Metropolitan University Yoshikazu Mizuguchi Department of Physics, Tokyo Metropolitan University Tomohiro Matsushita Nara Institute of Science and Technology (NAIST) Takanori Wakita Graduate School of Natural Science and Technology, Okayama University Yuji Muraoka Graduate School of Natural Science and Technology, Okayama University Takayoshi Yokoya Graduate School of Natural Science and Technology, Okayama University La(O,F)BiS2-xSex is a layered material that is considered to be a candidate exotic superconductor as well as a promising thermoelectrical material. We performed soft X-ray photoelectron holography to study the Se incorporation site and the local atomic arrangement of the conducting layer. A comparison of the experimental holograms with the simulated holograms indicates that Se atoms preferentially occupy the S sites in the conducting Bi–S plane of La(O,F)BiS2. A comparison between the state-of-the-art holographic reconstructions of La(O,F)BiSSe and La(O,F)BiS2 suggests that Se substitution suppresses the displacement of S atoms in La(O,F)BiS2. These results provide photoelectron holographic evidence for the Se incorporation site and the Se-induced suppression of in-plane disorder. No potential conflict of interest relevant to this article was reported.

岡山大学全学教育・ 学生支援機構 Acta Medica Okayama 2432-9665 6 2021 Advances in Superconductivity as a road to meet Energy and Health SDGs: joint Japanese and European research teams may take the lead 148 165 EN Toshihiko Kiwa Okayama University Takayoshi Yokoya Okayama University Bernard Chenevier Okayama University Valeria Di Cosmo University of Turin Marco Truccato University of Turin William Sacks Sorbonne University, Faculty of Science and Engineering, Paris Wolfgang Sauerwein DGBNCT (Deutsche Gesellschaft für Bor-Neutroneneinfangtherapie e.V.) and University of Duisburg-Essen 10.18926/63338 Based on a statistical analysis of R&D activities in the field of superconductivity (SC) in a broad sense, the paper reports that Japan's leadership is strong over the past 20 years, in terms of researchers publications and patents. It also essentially shows that among the main world players, the Japanese normalized contribution is significantly dominating, although some trend towards a diminished leadership is observed in the data over the period 2005 -present time. Finally, the paper highlights that by taking advantage of their internationally recognized expertise in the field, joint Japanese and European research teams may advance superconductivity as a reliable road to meet Energy and Health SDGs (Sustainable Development Goals -UNESCO 2015). No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0953-8984 33 3 2020 Soft x-ray irradiation induced metallization of layered TiNCl 035501 EN Noriyuki Kataoka Graduate School of Natural Science and Technology, Okayama University Masashi Tanaka Graduate School of Engineering, Kyushu Institute of Technology Wataru Hosoda Graduate School of Natural Science and Technology, Okayama University Takumi Taniguchi Graduate School of Natural Science and Technology, Okayama University Shin-ichi Fujimori Materials Sciences Research Center, Japan Atomic Energy Agency Takanori Wakita Graduate School of Natural Science and Technology, Okayama University Yuji Muraoka Graduate School of Natural Science and Technology, Okayama University Takayoshi Yokoya Graduate School of Natural Science and Technology, Okayama University We have performed soft x-ray spectroscopy in order to study the photoirradiation time dependence of the valence band structure and chemical states of layered transition metal nitride chloride TiNCl. Under the soft x-ray irradiation, the intensities of the states near the Fermi level (EF) and the Ti3+ component increased, while the Cl 2p intensity decreased. Ti 2p–3d resonance photoemission spectroscopy confirmed a distinctive Fermi edge with Ti 3d character. These results indicate the photo-induced metallization originates from deintercalation due to Cl desorption, and thus provide a new carrier doping method that controls the conducting properties of TiNCl. No potential conflict of interest relevant to this article was reported.

Nature Acta Medica Okayama 2045-2322 10 1 2020 Skewed electronic band structure induced by electric polarization in ferroelectric BaTiO3 10702 EN Norihiro Oshime Graduate School of Natural Science and Technology, Okayama University Jun Kano Graduate School of Natural Science and Technology, Okayama University Eiji Ikenaga Japan Synchrotron Radiation Research Institute, JASRI Shintaro Yasui Laboratory for Materials and Structures, Tokyo Institute of Technology Yosuke Hamasaki Laboratory for Materials and Structures, Tokyo Institute of Technology Sou Yasuhara Laboratory for Materials and Structures, Tokyo Institute of Technology Satoshi Hinokuma Innovative Oxidation Team, Interdisciplinary Research Center for Catalytic Chemistry, National Institute of Advanced Industrial Science and Technology Naoshi Ikeda Graduate School of Natural Science and Technology, Okayama University Pierre-Eymeric Janolin Université Paris-Saclay,CentraleSupélec, CNRS, Laboratoire SPMS Jean-Michel Kiat Université Paris-Saclay,CentraleSupélec, CNRS, Laboratoire SPMS Mitsuru Itoh Laboratory for Materials and Structures, Tokyo Institute of Technology Takayoshi Yokoya GResearch Institute for Interdisciplinary Science, Okayama University Tatsuo Fujii Graduate School of Natural Science and Technology, Okayama University Akira Yasui Japan Synchrotron Radiation Research Institute, JASRI Hitoshi Osawa Japan Synchrotron Radiation Research Institute, JASRI Skewed band structures have been empirically described in ferroelectric materials to explain the functioning of recently developed ferroelectric tunneling junction (FTJs). Nonvolatile ferroelectric random access memory (FeRAM) and the artificial neural network device based on the FTJ system are rapidly developing. However, because the actual ferroelectric band structure has not been elucidated, precise designing of devices has to be advanced through appropriate heuristics. Here, we perform angle-resolved hard X-ray photoemission spectroscopy of ferroelectric BaTiO3 thin films for the direct observation of ferroelectric band skewing structure as the depth profiles of atomic orbitals. The depth-resolved electronic band structure consists of three depth regions: a potential slope along the electric polarization in the core, the surface and interface exhibiting slight changes. We also demonstrate that the direction of the energy shift is controlled by the polarization reversal. In the ferroelectric skewed band structure, we found that the difference in energy shifts of the atomic orbitals is correlated with the atomic configuration of the soft phonon mode reflecting the Born effective charges. These findings lead to a better understanding of the origin of electric polarization. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0040-6090 698 2020 Strain effects on spinodal decomposition in TiO2-VO(2)films on TiO2(100) substrates 137854 EN Yuji Muraoka Research Institute for Interdisciplinary Science (RIIS), Okayama University Fumiya Yoshii Graduate School of Natural Science and Technology, Okayama University Takahiro Fukuda Graduate School of Natural Science and Technology, Okayama University Yuji Manabe Graduate School of Natural Science and Technology, Okayama University Mikiko Yasuno Graduate School of Natural Science and Technology, Okayama University Yoshito Takemoto Graduate School of Natural Science and Technology, Okayama University Kensei Terashima Research Institute for Interdisciplinary Science, Okayama University Takanori Wakita Research Institute for Interdisciplinary Science (RIIS), Okayama University Takayoshi Yokoya We investigate the influence of lattice strain in the c-axis direction on spinodal decomposition in rutile TiO2-VO2 films on TiO2(100) substrates. The [100]-oriented Ti0.4V0.6O2 (TVO) solid-solution films are fabricated on rutile TiO2(100) substrates using a pulsed laser deposition with a KrF excimer laser, and are annealed inside the spinodal region. X-ray diffraction and scanning transmission electron microscopy are employed for characterization. Consequently, the in-plane tensile strain in the c-axis direction promotes the Ti-V interdiffusion in TVO/TiO2(100) under thermal annealing. In contrast, relaxation of the tensile strain results in the occurrence of spinodal decomposition along the c-axis direction in the film. These results indicate that the relaxation of the tensile strain in the c-axis direction is critically important for enabling spinodal decomposition in TVO/TiO2(100). Our work helps deepen the understanding of spinodal decomposition in the TVO film and provides information on achieving novel nanostructures via spinodal decomposition in TVO/TiO2(100). No potential conflict of interest relevant to this article was reported.

Nature Publishing Group Acta Medica Okayama 2045-2322 9 2019 Fermi level tuning of Ag-doped Bi2Se3 topological insulator 5376 EN Eri Uesugi Research Institute for Interdisciplinary Science, Okayama University Takaki Uchiyama Research Institute for Interdisciplinary Science, Okayama University Hidenori Goto Research Institute for Interdisciplinary Science, Okayama University Hiromi Ota Advanced Science Research Centre, Okayama University Teppei Ueno Research Institute for Interdisciplinary Science, Okayama University Hirokazu Fujiwara Research Institute for Interdisciplinary Science, Okayama University Kensei Terashima Research Institute for Interdisciplinary Science, Okayama University Takayoshi Yokoya Research Institute for Interdisciplinary Science, Okayama University Fumihiko Matsui Graduate School of Materials Science, Nara Institute of Science and Technology Jun Akimitsu Research Institute for Interdisciplinary Science, Okayama University Kaya Kobayashi Research Institute for Interdisciplinary Science, Okayama University Yoshihiro Kubozono Research Institute for Interdisciplinary Science, Okayama University The temperature dependence of the resistivity (rho) of Ag-doped Bi2Se3 (AgxBi2-xSe3) shows insulating behavior above 35 K, but below 35 K, rho suddenly decreases with decreasing temperature, in contrast to the metallic behavior for non-doped Bi2Se3 at 1.5-300 K. This significant change in transport properties from metallic behavior clearly shows that the Ag doping of Bi2Se3 can effectively tune the Fermi level downward. The Hall effect measurement shows that carrier is still electron in AgxBi2-xSe3 and the electron density changes with temperature to reasonably explain the transport properties. Furthermore, the positive gating of AgxBi2-xSe3 provides metallic behavior that is similar to that of non-doped Bi2Se3, indicating a successful upward tuning of the Fermi level. No potential conflict of interest relevant to this article was reported.

American Chemical Society Acta Medica Okayama 15306984 19 9 2019 Asymmetric Phosphorus Incorporation in Homoepitaxial P-Doped (111) Diamond Revealed by Photoelectron Holography 5915 5919 EN T. Yokoya Research Institute for Interdisciplinary Science (RIIS), Okayama University K. Terashima Research Institute for Interdisciplinary Science (RIIS), Okayama University A. Takeda Graduate School of Science and Technology, Okayama University T. Fukura Graduate School of Science and Technology, Okayama University H. Fujiwara Graduate School of Science and Technology, Okayama University T. Muro Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8 T. Kinoshita Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8 H. Kato Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) S. Yamasaki Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) T. Oguchi Institute of Scientific and Industrial Research, Osaka University T. Wakita Research Institute for Interdisciplinary Science (RIIS), Okayama University Y. Muraoka Research Institute for Interdisciplinary Science (RIIS), Okayama University T. Matsushita Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8 Diamond has two crystallographically inequivalent sites in the unit cell. In doped diamond, dopant occupation in the two sites is expected to be equal. Nevertheless, preferential dopant occupation during growth under nonequilibrium conditions is of fundamental importance, for example, to enhance the properties of nitrogen-vacancy (N-V) centers; therefore, this is a promising candidate for a qubit. However, the lack of suitable experimental techniques has made it difficult to study the crystal- and chemical-site-resolved local structures of dopants. Here, we confirm the identity of two chemical sites with asymmetric dopant incorporation in the diamond structure, via the photoelectron holography (PEH) of heavily phosphorus (P)-doped diamond prepared by chemical vapor deposition. One is substitutionally incorporated P with preferential site occupations and the other can be attributed to a PV split vacancy complex with preferential orientation. The present study shows that PEH is a valuable technique to study the local structures around dopants with a resolution of crystallographically inequivalent but energetically equivalent sites/orientations. Such information provides strategies to improve the properties of dopant related-complexes in which alignment is crucial for sensing of magnetic field or quantum spin register using N-V centers in diamond. No potential conflict of interest relevant to this article was reported.

The American Physical Society Acta Medica Okayama 1098-0121 90 22 2014 Proximity to Fermi-surface topological change in superconducting LaO0.54F0.46BiS2 EN Kensei Terashima Junki Sonoyama Takanori Wakita Masanori Sunagawa Kanta Ono Hiroshi Kumigashira Takayuki Muro Masanori Nagao Satoshi Watauchi Isao Tanaka Hiroyuki Okazaki Yoshihiko Takano Osuke Miura Yoshikazu Mizuguchi Hidetomo Usui Katsuhiro Suzuki Kazuhiko Kuroki Yuji Muraoka Takayoshi Yokoya The electronic structure of nearly optimally doped novel superconductor LaO1−xFxBiS2(x = 0.46) was investigated using angle-resolved photoemission spectroscopy (ARPES). We clearly observed band dispersions from 2 to 6 eV binding energy and near the Fermi level (EF), which are well reproduced by first-principles calculations when the spin-orbit coupling is taken into account. The ARPES intensity map near EF shows a squarelike distribution around the (Z) point in addition to electronlike Fermi-surface (FS) sheets around the X(R) point, indicating that FS of LaO0.54F0.46BiS2 is in close proximity to the theoretically predicted topological change. No potential conflict of interest relevant to this article was reported.

American Institute of Physics. Acta Medica Okayama 0003-6951 98 8 2011 Multiple phosphorus chemical sites in heavily phosphorus-doped diamond 082107-1 082107-3 EN Hiroyuki Okazaki Rikiya Yoshida Takayuki Muro Tetsuya Nakamura Takanori Wakita Yuji Muraoka Masaaki Hirai Hiromitsu Kato Satoshi Yamasaki Yoshihiko Takano Satoshi Ishii Tamio Oguchi Takayoshi Yokoya We have performed high-resolution core level photoemission spectroscopy on a heavily phosphorus (P)-doped diamond film in order to elucidate the chemical sites of doped-phosphorus atoms in diamond. P 2p core level study shows two bulk components, providing spectroscopic evidence for multiple chemical sites of doped-phosphorus atoms. This indicates that only a part of doped-phosphorus atoms contribute to the formation of carriers. From a comparison with band calculations, possible origins for the chemical sites are discussed. No potential conflict of interest relevant to this article was reported.

American Institute of Physics. Acta Medica Okayama 0021-8979 109 4 2011 Spectroscopic evidence of the formation of (V,Ti)O₂ solid solution in VO₂ thinner films grown on TiO₂(001) substrates 043702-1 043702-6 EN Y. Muraoka K. Saeki R. Eguchi T. Wakita M. Hirai T. Yokoya S. Shin We have prepared VO2 thin films epitaxially grown on TiO2(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO2 itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO2 substrates, with a chemical state similar to that in (V,Ti)O-2 solid solution. These results indicate that insulating (V,Ti)O-2 solid solution is formed in the thinner films. We propose a simple growth model of a VO2 thin film on a TiO2(001) substrate. Near the interface, insulating (V,Ti) O-2 solid solution is formed due to the diffusion of Ti ions from the TiO2 substrate into the VO2 film. The concentration of Ti in (V,Ti) O-2 is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO2 thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO2 thin films and TiO2 substrates is a key issue to study the physical property of an ultrathin film of "pure" VO2, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations. No potential conflict of interest relevant to this article was reported.

American Institute of Physics. Acta Medica Okayama 0021-8979 108 4 2010 Bulk and surface physical properties of a CrO₂ thin film prepared from a Cr₈O₂₁ precursor 043916-1 043916-4 EN K. Iwai Y. Muraoka T. Wakita M. Hirai T. Yokoya Y. Kato T. Muro Y. Tamenori We have prepared a CrO(2) thin film by chemical vapor deposition from a Cr(8)O(21) precursor and studied the bulk and surface physical properties. The CrO(2) thin film is grown on a TiO(2) (100) substrate by heating of a Cr(8)O(21) precursor and TiO(2) (100) substrate together in a sealed quartz tube. The prepared film is found from x-ray diffraction analysis to be an (100)-oriented single phase. The magnetization and resistivity measurements indicate that the film is a ferromagnetic metal with a Curie temperature of about 400 K. Cr 3s core-level and valence band photoelectron spectroscopy spectra reveal the presence of a metallic CrO(2) in the surface region of the film. Our work indicates that preparation from a Cr(8)O(21) precursor is promising for obtaining a CrO(2) thin film with the metallic surface. No potential conflict of interest relevant to this article was reported.

American Institute of Physics. Acta Medica Okayama 0021-8979 107 7 2010 Room temperature ferromagnetic behavior in the hollandite-type titanium oxide 073910-1 073910-6 EN K. Noami Y. Muraoka T. Wakita M. Hirai Y. Kato T. Muro Y. Tamenori T. Yokoya A hollandite-type K(x)Ti(8)O(16) polycrystalline sample has been prepared and studied by magnetization, resistivity and x-ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behavior is observed in the magnetic hysteresis measurement. The sample shows a semiconductive temperature dependence in the resistivity measurement. Analysis of the Ti 2p(3/2) core-level XPS spectrum indicates that the titanium ions have a mixed valence of Ti(4+) and Ti(3+). In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti(3+) ions in the hollandite-type TiO(2) lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type K(x)Ti(8)O(16) sample can be classified as a TiO(2)-based wide-gap semiconductor with Curie temperature above room temperature. Room temperature ferromagnetism (RTFM) decreases in the sample prepared under a strong reducing gas atmosphere, accompanied with the decrease in the resistivity. The results imply that the localized 3d electrons are responsible for the RTFM of the K(x)Ti(8)O(16) sample. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 0022-3697 72 5 2011 Photoemission study of electronic structure evolution across the metal-insulator transition of heavily B-doped diamond 582 584 EN H. Okazaki T. Arakane K. Sugawara T. Sato T. Takahashi T. Wakita M. Hirai Y. Muraoka Y. Takano S. Ishii S. Iriyama H. Kawarada T. Yokoya We studied the electronic structure evolution of heavily B-doped diamond films across the metal-insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (E(F)) up to similar to 5k(B)T can be observed (k(B) is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near E(F). Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of E(F), can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0921-4534 470 S1 2010 Photoemission study of Ca-intercalated graphite superconductor CaC₆ S637 S638 EN Hiroyuki Okazaki Rikiya Yoshida Keisuke Iwai Kengo Noami Takayuki Muro Tetsuya Nakamura Takanori Wakita Yuji Muraoka Masaaki Hirai Fumiaki Tomioka Yoshihiko Takano Asami Takenaka Masahiro Toyoda Tamio Oguch Takayoshi Yokoya In this work, we have performed resonant photoemission studies of Ca-intercalated graphite superconductor CaC6. Using photon energy of the Ca 2p-3d threshold, the photoemission intensity of the peak at Fermi energy (E-F) is resonantly enhanced. This result provides spectroscopic evidence for the existence of Ca 3d states at E-F, and strongly supports that Ca 3d state plays a crucial role for the superconductivity of this material with relatively high T-c. No potential conflict of interest relevant to this article was reported.

The Physical Society of Japan Acta Medica Okayama 0031-9015 79 12 2010 Electronic Structure of the Novel Filled Skutterudite PrPt₄Ge₁₂ Superconductor 124701-1 124701-4 EN Yoshiaki Nakamura Hiroyuki Okazaki Rikiya Yoshida Takanori Wakita Masaaki Hirai Yuji Muraoka Hiroyuki Takeya Kazuto Hirata Hiroshi Kumigashira Masaharu Oshima Takayoshi Yokoya We have performed soft x-ray photoemission spectroscopy (SXPES) and resonant photoemission spectroscopy (RPES) of the filled skutterudite superconductor PrPt₄Ge₁₂ in order to study the electronic structure of valence band and the character of Pr 4f. SXPES of PrPt₄Ge₁₂ measured with 1200 eV photon energy, where spectral contribution of Pr 4f is negligible, was found nearly identical with that of LaPt₄Ge₁₂, indicating similarity of Pt–Ge derived electronic states of the two compounds. Good correspondence with band calculations allows us to ascribe the dominant Ge 4p character of the density of states at the Fermi level (E_F). Pr 3d → 4f RPES shows that, although Pr 4f electrons in PrPt₄Ge₁₂ are not as strongly hybridized with conduction electrons near E_F as in PrFe4P12, there are finite Pr 4f contribution to the states near E_F in PrPt₄Ge₁₂. These PES results give the information of fundamental electronic structure for understanding the physical properties of the novel filled skutterudite superconductor PrPt₄Ge₁₂. No potential conflict of interest relevant to this article was reported.

The American Physical Society Acta Medica Okayama 1098-0121 86 1 2012 Comparative photoemission studies on the superconducting gap of the filled skutterudite superconductors LaPt₄Ge₁₂ and PrPt₄Ge₁₂ 014521-1 014521-5 EN Yoshiaki Nakamura Hiroyuki Okazaki Rikiya Yoshida Takanori Wakita Hiroyuki Takeya Kazuto Hirata Masaaki Hirai Yuji Muraoka Takayoshi Yokoya We performed a comparative study of the superconducting gap in the new filled skutterudite superconductors LaPt₄Ge₁₂ and PrPt₄Ge₁₂ using high-resolution photoemission spectroscopy. We succeeded in observing spectral changes across Tc that reflect the opening of the superconducting gap in both compounds and also in observing a noticeable difference in their respective superconducting spectral shapes near the Fermi level, pointing toward a more complex superconducting gap structure in PrPt₄Ge₁₂. In addition, we found that the two-gap model is more suitable for describing the superconducting-state spectrum of PrPt₄Ge₁₂ than the single-isotropic-gap and single-anisotropic-gap models, which suggests an explanation that multiband effects may possibly induce the anomalous superconducting properties of PrPt₄Ge₁₂. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 0022-3697 72 5 2011 Ultrahigh-resolution laser photoemission study of URu₂Si₂ across the hidden-order transition 580 581 EN Rikiya Yoshida Yoshiaki Nakamura Masaki Fukui Yoshinori Haga Etsuji Yamamoto Yoshichika Ōnuki Mario Okawa Shik Shin Masaaki Hirai Yuji Muraoka Takayoshi Yokoya We have studied the electronic structures of URu₂Si₂ employing ultrahigh-resolutionlaser angle-resolved photoemission spectroscopy. The change of photoemission spectra is investigated across the hidden-ordertransition, and the emergence of a narrow band is clearly observed near the Fermi level for both (π,0) and (π,π) directions. In addition, it is shown that tuning of light's polarization allows the signal of a hole-like dispersive feature to enhance. These observations prove that laser angle-resolved photoemission spectroscopy is an effective tool for studying the evolution of electronic structures across the hidden-ordertransition in URu₂Si₂. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0921-4534 470 S1 2010 Analysis on photoemission spectrum of superconducting FeSe S389 S390 EN Rikiya Yoshida Takanori Wakita Hiroyuki Okazaki Yoshikazu Mizuguchi Shunsuke Tsuda Yoshihiko Takano Hiroyuki Takeya Kazuto Hirata Yukako Kato Takayuki Muro Mario Okawa Kyoko Ishizaka Shik Shin Hisatomo Harima Masaaki Hirai Yuji Muraoka Takayoshi Yokoya In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around E(B) = 2 eV. This result suggests the necessity of theoretical treatment beyond local density approximation. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0921-4534 470 S1 2010 Angle-resolved photoemission study of Si electronic structure: Boron concentration dependence S641 S643 EN Takanori Wakita Hiroyuki Okazaki Yoshihiko Takano Masaaki Hirai Yuji Muraoka Takayoshi Yokoya The boron concentration dependence of the Si electronic structure of Si(100)2 × 1 surfaces were investigated by angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra exhibit rigid shifts toward lower binding energy as the boron concentration increases. The band dispersion was obtained from fitting procedure, and it is found that the top of the valence band does not exceed the Fermi level even with a boron concentration 35 times larger than the critical concentration of the metal-insulator transition. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0368-2048 181 2-3 2010 Angle-resolved photoemission spectroscopy for VO₂ thin films grown on TiO₂ (0 0 1) substrates 249 251 EN Y Muraoka K Saeki Y Yao T Wakita M Hirai T Yokoya R Eguchi S Shin We present the results of angle-resolved photoemission spectroscopy (ARPES) measurements of metallic VO₂ thin films. The VO₂ thin films have been grown on TiO₂ (0 0 1) single crystal substrates using pulsed laser deposition. The films exhibit a first-order metal–insulator transition (MIT) at 305 K. In the ARPES spectra of the metallic phase for the films, the O 2p band shows highly dispersive feature in the binding energy range of 3–8 eV along the Г–Z direction. The periodicity of the dispersive band is found to be 2.2 Å^-1 which is almost identical with the periodicity expected from the c-axis length of the VO₂ thin films. The overall feature of the experimental band structure is similar to the band structure calculations, supporting that we have succeeded in observing the dispersive band of the O 2p state in the metallic VO₂ thin film. The present work indicates that the ARPES measurements using epitaxial thin films are promising for determining the band structure of VO₂. No potential conflict of interest relevant to this article was reported.

International Union of Crystallography Acta Medica Okayama 0909-0495 18 6 2011 Development of a soft X-ray angle-resolved photoemission system applicable to 100 µm crystals 879 884 EN Takayuki Muro yukako Kato Tomohiro Matsushita Toyohiko Kinoshita Yoshio Watanabe Hiroyuki Okazaki Takayoshi Yokoya Akira Sekiyama higemasa Suga A system for angle-resolved photoemission spectroscopy (ARPES) of small single crystals with sizes down to 100 µm has been developed. Soft X-ray synchrotron radiation with a spot size of ～40 µm × 65 µm at the sample position is used for the excitation. Using this system an ARPES measurement has been performed on a Si crystal of size 120 µm × 100 µm × 80 µm. The crystal was properly oriented on a sample stage by measuring the Laue spots. The crystal was cleaved in situ with a microcleaver at 100 K. The cleaved surface was adjusted to the beam spot using an optical microscope. Consequently, clear band dispersions along the Γ-X direction reflecting the bulk electronic states were observed with a photon energy of 879 eV. No potential conflict of interest relevant to this article was reported.

The American Physical Society Acta Medica Okayama 1098-0121 82 20 2010 Signature of hidden order and evidence for periodicity modification in URu₂Si₂ 205108-1 205108-6 EN Rikiya Yoshida Yoshiaki Nakamura Masaki Fukui Yoshinori Haga Etsuji Yamamoto Yoshichika Onuki Mario Okawa Shik Shin Masaaki Hirai Yuji Muraoka Takayoshi Yokoya The detail of electronic structures near the Fermi level in URu₂Si₂ has been investigated employing state-of-art laser angle-resolved photoemission spectroscopy. The observation of a narrow dispersive band near the Fermi level in the ordered state as well as its absence in a Rh-substituted sample strongly suggest that the emergence of the narrow band is a clear signature of the hidden-order transition. The temperature dependence of the narrow band, which appears at the onset of the hidden-order transition, invokes the occurrence of periodicity modification in the ordered state, which is shown for the first time by any spectroscopic probe. We compare our data to other previous studies and discuss possible implications. No potential conflict of interest relevant to this article was reported.

The American Physical Society Acta Medica Okayama 1098-0121 82 19 2010 Electronic structure of pristine and K-doped solid picene: Nonrigid band change and its implication for electron-intramolecular-vibration interaction 195114-1 195114-5 EN H Okazaki T Wakita T Muro Y Kaji X Lee H Mitamura N Kawasaki Y Kubozono Y Yamanari T Kambe T Kato M Hirai Y Muraoka T Yokoya We use photoemission spectroscopy to study electronic structures of pristine and K-doped solid picene. The valence band spectrum of pristine picene consists of three main features with no state at the Fermi level (E_F) while that of K-doped picene has three structures similar to those of pristine picene with new states near E_F, consistent with the semiconductor-metal transition. The K-induced change cannot be explained with a simple rigid-band model of pristine picene but can be interpreted by molecular-orbital calculations considering electron-intramolecular-vibration interaction. Excellent agreement of the K-doped spectrum with the calculations points to importance of electron-intramolecular-vibration interaction in K-doped picene. No potential conflict of interest relevant to this article was reported.

The American Physical Society Acta Medica Okayama 1098-0121 81 18 2010 Angle-resolved photoemission observation of the superconducting-gap minimum and its relation to the nesting vector in the phonon-mediated superconductor YNi₂B₂C 180509-1 180509-4 EN T Baba T Yokoya S Tsuda T Watanabe M Nohara H Takagi T Oguchi S Shin We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy to directly study the large superconducting (SC) gap anisotropy of YNi₂B₂C. We succeed in measuring momentum (k) dependence of SC gap for individual Fermi surface (FS) sheets, which demonstrates complexity of SC gap in a phonon-mediated superconductor. Within measured k regions on FS sheets, we find a pointlike minimum of SC gap, whose k positions can be connected by the known nesting vector. This shows close correlation between the nesting vector and node formation. No potential conflict of interest relevant to this article was reported.