Effect of Crystal Structure to Resonant X-Ray Scattering on YTiO3

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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.