Theory of orbital ordering and X-ray absorption linear dichroism in LaMnO3

On the basis of exact diagonalization of a single-ion Hamiltonian including the intra-atomic multipole interactions, we calculated Mn and Ti L-2.3 X-ray absorption linear dichroism (XLD) spectra for LaMnO3 and YTiO3, where antiferro-orbital ordering among the degenerate e(g) and t(2g) states, respectively, are reported. For the orbital polarization given by a superposition of the doubly degenerate eg states, the superposition is shown to be reflected in the integrated XLD intensity, while, in the case of the triply degenerate t(2g) states, the superposition is shown to be reflected in both the integrated intensity and the spectral shape, i.e. XLD is a promising method to observe details of orbital polarization. (C) 2004 Elsevier B.V. All rights reserved.