Interplay between Raman and fluorescence-like components in resonant X-ray emission spectra of degenerate d⁰ and d¹ systems

Resonant X-ray emission spectra (RXES) are theoretically studied with a doubly-degenerate one-dimensional periodic Anderson model under d0 and d1 fillings, together with normal X-ray emission spectra (NXES) and X-ray absorption spectra (XAS). The model is regarded as a simplified model of band insulators such as TiO2, and Mott-Hubbard insulators such as Ti2O3. Comparing with nondegenerate model calculations, we point out the important role of orbital degeneracy in reproducing experimental excitation energy dependence of RXES. The calculated results exhibit interplay between Raman and fluorescence-like components in both band insulator and Mott-Hubbard insulator. The former and latter components reflect the local point symmetry and the translational symmetry of the system, respectively. Our results qualitatively well explain Ti 3d-2p RXES of TiO2 and Ti2O3.