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Onishi, Hiroaki; Hotta, Takashi
AIP Conference Proceedings 850, p.1075 - 1076, 2006/09
We investigate the ground-state property of a 
-orbital Hubbard model on a triangular lattice at electron density 5.5 by using numerical techniques. There appears several types of paramagnetic phases, but we observe in common that one or two orbitals among three orbitals become relevant due to the effect of orbital ordering. It is found that charge stripe stabilized by the nearest-neighbor Coulomb interaction consists of antiferromagnetic/ferro-orbital chains for small Hund's coupling, while there occurs stripe charge ordering with ferromagnetic/antiferro-orbital chains for large Hund's coupling.
Cu
O
studied by resonant inelastic X-ray scatteringIshii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Kuzushita, Kaori; Inami, Toshiya; Owada, Kenji; Maekawa, Sadamichi*; Masui, Takahiko*; Tajima, Setsuko*; et al.
AIP Conference Proceedings 850, p.445 - 446, 2006/09
Mott gap excitations in the optimally doped high-
superconductor YBaCuO ( = 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the 
-plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the 
direction, while the excitation from the CuO plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO plane site.
Ce
CuO
(x=0, 0.075, and 0.15) studied by Resonant inelastic X-ray scatteringIshii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Maekawa, Sadamichi*; Hoesch, M.; Kuzushita, Kaori; Inami, Toshiya; Tsubota, Masami; Yamada, Kazuyoshi*; et al.
AIP Conference Proceedings 850, p.403 - 404, 2006/09
We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the electron-doped high- superconductor Nd
Ce
CuO. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with 
-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.
