Effect of crystal structure on resonant x-ray scattering in YTiO3

We investigate the mechanism of the resonant x-ray scattering on the Ti K edge region of YTiO3 using the band structure calculation combined with the local density approximation. A large intensity is obtained for the orbital superlattice spots. The calculated spectra consist of several peaks as a function of photon energy in agreement with the recent experiments. Against a naive interpretation that directly relates the intensity to the orbitally polarized 3d states, the obtained large intensity arises from the distorted crystal structure, i.e., the tilt of the TiO6 octahedra and the Jahn-Teller distortion, which considerably modifies the 4p states in the intermediate states of the dipolar process. This casts doubt on a prevailing assertion that the resonant x-ray scattering is a direct observation of the orbital order