Resonant Inelastic X-ray Scattering from Charge and Orbital Excitations in Manganites

We present a theory of the resonant inelastic x-ray scattering (RIXS) to study electronic excitations in orbital ordered manganites. The charge and orbital excitations of the Mn 3d electron are caused by the Coulomb interactions in the intermediate scattering state. The scattering cross section is formulated by the Liouville operator method where the local and itinerant natures of the excitations are taken into account on an equal footing. As a result, the cross section is expressed by the charge and orbital correlation functions associated with local corrections. The RIXS spectra are calculated numerically as functions of momentum and polarization of x ray. Through the calculations, we propose that RIXS provides a great opportunity to study the unique electronic excitations in correlated electron systems with orbital degeneracy.