Electronic excitations by resonant inelastic X-ray scattering

Ishii, Kenji; Yoshida, Masahiro; Jarrige, I.; Ikeuchi, Kazuhiko*; Murakami, Yoichi*; Mizuki, Junichiro; Ishihara, Sumio*; Tsutsui, Kenji; Toyama, Takami*; Maekawa, Sadamichi; Kudo, Kazutaka*; Koike, Yoji*; Endo, Yasuo*

In strongly correlated electron systems, such as transition metal oxides, it is widely recognized that the role of three degrees of freedom of the electron, i.e., charge, spin, and orbital are key ingredients to understand the electronic properties of these compounds. Among the degrees of freedom, dynamics of the spin in momentum-energy (Q-) space is studied by inelastic neutron scattering. On the other hand, photon is sensitive to the charge and its anisotropy, orbital, and therefore inelastic X-ray scattering (IXS) is suitable for the measurement of their excitations. In this sense, IXS can be considered as a complementary technique of the inelastic neutron scattering. Recently, brilliant X-rays from modern synchrotron radiation sources have enabled us to observe electronic excitations with IXS. Especially, resonant inelastic X-ray scattering (RIXS), where the incident photon energy is tuned near an absorption edge of a constituent element, has an advantage of significant resonant enhancement of inelastic signals and RIXS has been used to measure electronic excitations in strongly correlated electron systems. We will present our Cu K-edge RIXS works of charge-ordered SrCuO and orbital-ordered KCuF focusing on the charge and orbital excitations.