Theory of orbital excitation and resonant inelastic x-ray scattering in manganites

We study theoretically the collective orbital excitation called the orbital wave in the orbital ordered manganites. The dispersion relation of the orbital wave is strongly correlated with the static spin structure through the coupling between spin and orbital degrees of freedom. As a probe to detect the dispersion relation of the orbital wave, we propose possible excitation processes in the resonant inelastic x-ray scattering. The scattering cross section due to the orbital wave is calculated in several types of the orbital and spin structures.