Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502* Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan**
○takami Tohyama* Kenji Tsutsui** Sadamichi Maekawa**
Cu K-edge Resonant inelastic x-ray scattering (RIXS) in two-dimensional insulating cuprates reveals characteristic momentum dependence of a charge-transfer process from the occupied Zhang-Rice singlet band to the unoccupied upper Hubbard band, i.e., Mott-gap excitation. Using the numerically exact diagonalization technique for finite-size Hubbard cluster, we have proposed that the Mott-gap excitations are seen in the Cu K-edge RIXS even for doped cuprates but with different doping dependence between hole- and electron-doping . Recently we examined theoretically the Cu K-edge RIXS on electron-doped Nd2-xCexCuO4 and compared with the experimental data obtained in SPring-8. The low-energy spectrum is assigned as the intra-band excitation and is qualitatively similar to the dynamical charge correlation function . These results indicate that the RIXS is a powerful technique to investigate the charge dynamics in the strongly correlated electron systems. We also examine the momentum dependence of Cu L-edge RIXS in insulating cuprates . Using the two-band Hubbard model, we find that charge excitations characteristic of the Cu L-edge RIXS process appear in the spectrum.
 T. Tohyama, K. Tsutsui, S. Maekawa, J. Phys. Chem. Solids 66, 2139 (2005).
 K. Ishii, K. Tsutsui, et al, Phys. Rev. Lett. 94, 207003 (2005).
 K. Tsutsui, H. Yamamoto, T. Tohyama, S. Maekawa, J. Phys. Chem. Solids 67, 274 (2006).