American Physical Society Acta Medica Okayama 24699950 98 9 2018 Temperature-dependent local structure and superconductivity of BaPd2As2 and SrPd2As2 094525 EN K. Terashima Research Institute for Interdisciplinary Science, Okayama University E. Paris Dipartimento di Fisica, Universitá di Roma “La Sapienza” L. Simonelli CELLS - ALBA Synchrotron Radiation Facility E. Salas-Colera Spanish CRG BM25 Spline, ESRF - The European Synchrotron A. Puri CRG-LISA, ESRF T. Wakita Research Institute for Interdisciplinary Science, Okayama University Y. Yamada Research Institute for Interdisciplinary Science, Okayama University S. Nakano Research Institute for Interdisciplinary Science, Okayama University H. Idei Research Institute for Interdisciplinary Science, Okayama University K. Kudo Research Institute for Interdisciplinary Science, Okayama University M. Nohara Research Institute for Interdisciplinary Science, Okayama University Y. Muraoka Research Institute for Interdisciplinary Science, Okayama University T. Mizokawa Department of Applied Physics, Waseda University T. Yokoya Research Institute for Interdisciplinary Science, Okayama University N. L. Saini Dipartimento di Fisica, Universitá di Roma “La Sapienza” The local structures of 122-type paradium arsenides, namely BaPd2As2 and SrPd2As2, are examined by As K-edge extended x-ray absorption fine structure measurements to find a possible correlation between the variation of their superconducting transition temperature and the local structure. The local atomic distances are found to be consistent with average distances measured by diffraction techniques. The temperature dependence of mean square relative displacements reveal that, while BaPd2As2 is characterized by a local As-Pd soft mode, albeit with larger atomic disorder, SrPd2As2 shows anomalous As-Pd correlations with a kink at similar to 160 K due to hardening by raising temperature. We have discussed implications of these results and possible mechanisms of differing superconducting transition temperature in relation with the structural instability. No potential conflict of interest relevant to this article was reported.

American Physical Society Acta Medica Okayama 2469-9950 96 4 2017 Evolution of the remnant Fermi-surface state in the lightly doped correlated spin-orbit insulator Sr2-xLaxIrO4 041106 EN Kensei Terashima Research Institute for Interdisciplinary Science, Okayama University M. Sunagawa Graduate School of Natural Sciences, Okayama University H. Fujiwara Graduate School of Natural Sciences, Okayama University T. Fukura M. Fujii Graduate School of Natural Sciences, Okayama University K. Okada Aoyama Gakuin University K. Horigane Research Institute for Interdisciplinary Science, Okayama University K. Kobayashi Research Institute for Interdisciplinary Science, Okayama University R. Horie Research Institute for Interdisciplinary Science, Okayama University J. Akimitsu Research Institute for Interdisciplinary Science, Okayama University E. Golias Helmholtz-Zentrum Berlin für Materialien und Energie D. Marchenko Helmholtz-Zentrum Berlin für Materialien und Energie A. Varykhalov Helmholtz-Zentrum Berlin für Materialien und Energie N. L. Saini Dipartimento di Fisica, Universitá di Roma “La Sapienza T. Wakita Research Institute for Interdisciplinary Science, Okayama University Y. Muraoka Research Institute for Interdisciplinary Science, Okayama University T. Yokoya Research Institute for Interdisciplinary Science, Okayama University The electronic structure of the lightly electron-doped correlated spin-orbit insulator Sr2IrO4 has been studied by angle-resolved photoelectron spectroscopy. We have observed the coexistence of a lower Hubbard band and an in-gap band; the momentum dependence of the latter traces that of the band calculations without on-site Coulomb repulsion. The in-gap state remained anisotropically gapped in all observed momentum areas, forming a remnant Fermi-surface state, evolving towards the Fermi energy by carrier doping. These experimental results show a striking similarity with those observed in deeply underdoped cuprates, suggesting the common nature of the nodal liquid states observed in both compounds. 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.

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.

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.

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.

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.

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.