Resonant inelastic X-ray scattering in strongly correlated electron systems

Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Inami, Toshiya; Owada, Kenji; Kuzushita, Kaori*; Hoesch, M.; Tsubota, Masami; Mizuki, Junichiro; Murakami, Yoichi; Maekawa, Sadamichi*; Masui, Takahiko*; Tajima, Setsuko*; Yamada, Kazuyoshi*

Resonant inelastic X-ray scattering studies on high- superconductors NdCeCuO and YBaCuO are presented. In NdCuO and YBaCuO, which are Mott insulators, an excitation across the Mott gap is observed around 2 eV. The spectral weight of this excitation shifts to higher energy with increasing the momentum transfer and the dispersion of the excitation is larger along the direction than the direction. An intraband excitation in the upper Hubbard band emerges in the spectra of electron-doped NdCeCuO. As a function of the momentum transfer in the CuO plane, the excitation shifts to higher energy up to 2-2.5 eV at the zone boundary, accompanied by an increase of the spectral width. On the other hand, excitations from two inequivalent Cu sites in hole-doped YBaCuO are distinguished by the momentum dependence and the Mott gap of the CuO chain site is found to be much smaller than that of the CuO plane site.