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225 results on '"Usuda M"'

1. Magnetic Resonant X-Ray Scattering in KCuF3

Author

Takahashi, M., Usuda, M., and Igarashi, J.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We study the magnetic resonant x-ray scattering (RXS) spectra around the $K$ edge of Cu in KCuF$_3$ on the basis of an {\em ab initio} calculation. We use the full-potential linearlized augmented plane wave method in the LDA$+U$ scheme, and introduce the lattice distortion as inputs of the calculation. We obtain finite intensity on magnetic superlattice spots, about three orders of magnitude smaller than on orbital superlattice spots, by taking account of the spin-orbit interaction (SOI). No intensity appears without the SOI, indicating that the intensity arises not from the spin polarization but from the orbital polarization in $4p$ states. The present calculation reproduces well the experimental spectra as functions of photon energy and of azimuthal angle. We also calculate the RXS intensity on orbital superlattice spots. It is found that the intensity increases with increasing Jahn-Teller distortion. The spectra remain nearly the same in the nonmagnetic state given by the simple LDA, in which the orbital polarization in the 3d states is much smaller. This strongly suggests that the intensity on orbital spots is mainly controlled by the lattice distortion, not by the 3d orbital order itself., Comment: 7 pages, 8 figures, Submitted to PRB, RevTeX4

Published
2002
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18. Role of Ag doping in Ba8Si46 compounds

Author

Kamakura, N., Nakano, T., Ikemoto, Y., Usuda, M., Fukuoka, Hiroshi, Yamanaka, Shoji, Shin, S., and Kobayashi, K.

Abstract

The silicon clathrate compound Ba8Si46 shows superconductivity below the critical temperature (Tc) of 8K, and the Tc decreases monotonically with doping Ag. In order to reveal effects of Ag doping on the electronic states, we have applied soft x-ray photoemission spectroscopy to Ag-doped silicon clathrate compounds Ba8AgxSi46-x (x=0,1,3,6). The valence band photoemission spectra show that a Ba 5d-derived state at the Fermi level (EF), which is prominently observed in Ba8Si46, decreases with increasing Ag content. The reduction in the peak intensity at EF with increasing Ag content is therefore in accord with the decrease of Tc in Ba8AgxSi46-x. Band structure calculation using local-density approximation reproduces the observed valence band spectra of x=0 and 6. The Si 2p and Ba 4d core-level photoemission spectra demonstrate that the valence electron of Si is attracted to the Ag site in x=1 and the 5d electron of Ba inside the Si24 cage is further donated to Ag in x≥3. Hence, Ag doping leads to the reduction of the peak at EF.

Published
2005

19. Compton scattering study of the silicon clathrate Ba8Si 46 : Experiment and theory

Author

Itou, M., Sakurai, Y., Usuda, M., Cros, C., Fukuoka, Hiroshi, and Yamanaka, Shoji

Abstract

The Compton profile of the Ba doped silicon clathrate (Ba 8Si46) has been studied using the high-resolution Compton scattering technique. The Compton profile is sensitive to the change of wave functions, and the good agreement between experiment and theory validates a theoretical prediction. A difference Compton profile between the Ba doped and nondoped clathrates (Si136) has been experimentally obtained and compared with that of a first-principles band structure calculation. The experiment and calculation show excellent agreement with respect to the overall shape in the profile. Analyses of partial density of the states (DOS) predict that, by doping Ba atoms into the Si cages, Ba 6s electrons are transferred into Ba 5d orbitals that are strongly hybridized with Si 3p orbitals. The hybridized states form a sharp peak of the DOS in close vicinity of the Fermi level, which plays an important role for the occurrence of superconductivity in Ba 8Si46.

Published
2005

20. Compton scattering of the silicon clathrate Ba8Si46: experiment and theory

Author

Itou, M., Sakurai, Y., Usuda, M., Cros, Christian, Fukuoka, H., Yamanaka, S., Japan Synchrotron Radiation Research Institute [Hyogo] (JASRI), Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut Polytechnique de Bordeaux-Université de Bordeaux (UB), Department of Applied Chemistry (Faculty of Engineering, Hiroshima University), and Hiroshima University

Subjects
PACS : 78.70.Ck, 71.15.Ap, 74.25.Jb, 74.70.Wz, [CHIM.MATE]Chemical Sciences/Material chemistry
Abstract

Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.) ; Critical currents ; Fullerenes and related materials ; X-ray scattering; Compton scattering technique. The Compton profile is sensitive to the change of wave functions, and the good agreement between experiment and theory validates a theoretical prediction. A difference Compton profile between the Ba doped and nondoped clathrates (Si136) has been experimentally obtained and compared with that of a first-principles band structure calculation. The experiment and calculation show excellent agreement with respect to the overall shape in the profile. Analyses of partial density of the states (DOS) predict that, by doping Ba atoms into the Si cages, Ba 6s electrons are transferred into Ba 5d orbitals that are strongly hybridized with Si 3p orbitals. The hybridized states form a sharp peak of the DOS in close vicinity of the Fermi level, which plays an important role for the occurrence of superconductivity in Ba8Si46.

Published
2005
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23. Dielectric functions and quasi-particle lifetimes in Ag: full-potential LMTO and LAPW GW approaches

Author

Eusko Jaurlaritza, Max Planck Society, Iberdrola, Ministerio de Educación y Cultura (España), Zhukov, Vladlen P., Usuda, M., Chulkov, Eugene V., Echenique, Pedro M., Eusko Jaurlaritza, Max Planck Society, Iberdrola, Ministerio de Educación y Cultura (España), Zhukov, Vladlen P., Usuda, M., Chulkov, Eugene V., and Echenique, Pedro M.

Abstract

We report theoretical studies of dielectric functions and quasi-particle lifetimes in Ag by means of ab initio full-potential linear ‘muffin-tin’-orbitals LMTO GW and LAPW approaches. We show that the methods provide better description of the dielectric functions then the previous studies based on local density approximation of the density functional theory. In particular, the calculated electron energy loss function contains plasmon absorption peak which was absent in earlier calculations. The computed lifetimes of holes in the highest d-states are in good agreement with the experimental data. At lower energy large discrepancy between calculated and experimental data is observed which we refer to neglecting the vertex corrections.

Published
2003

25. THE BLENDED HOLLOW FIBER KIDNEY (BHFK)

Author

Ohta, K., Maeda, K., Saito, A., Kobayashi, S., Sezaki, R., Shinzato, T., Usuda, M., Asada, H., Kobayashi, K., Nishi, H., Ito, K., and Yamamoto, Y.

Published
1978

27. Quantitative Measurement of the Spectral Function of Aluminum and Lithium by Electron Momentum Spectroscopy

Author

Vos, Maarten, Kheifets, Anatoli, Sashin, Vladimir, Weigold, Erich, Usuda, M, Aryasetiawan, Ferdi, Vos, Maarten, Kheifets, Anatoli, Sashin, Vladimir, Weigold, Erich, Usuda, M, and Aryasetiawan, Ferdi

Abstract

We present measurements of the spectral function of aluminum and lithium using high-energy electron momentum spectroscopy. For aluminum the quasiparticle peaks show clear asymmetries and significant satellite intensity that extends over a wide region to larger binding energies. The intensity distribution is not well described by band structure calculations. These data are described only by calculations based on the manybody cumulant expansion scheme. The measured momentum distribution at the Fermi level agrees with the theoretical one within 0.03 a.u. For lithium a bandwidth of 3.0 eV is obtained.

Published
2002

29. Role of Ag doping inBa8Si46compounds

Author

Kamakura, N., primary, Nakano, T., additional, Ikemoto, Y., additional, Usuda, M., additional, Fukuoka, H., additional, Yamanaka, S., additional, Shin, S., additional, and Kobayashi, K., additional

Published
2005
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