Spin-orbital effects in Mott-Hubbard optical bands in LaMnO3

The anisotropy of the lowest-energy optical band and the spectral-weight shifts induced by antiferromagnetic spin correlations are quantitatively described by an effective spin-orbital superexchange model. An analysis of the multiplet structure of the intersite transitions by Mn eg electrons allowed us to estimate the effective intra-atomic Coulomb interaction, the Hund exchange coupling, and the Jahn-Teller splitting energy between eg orbitals in LaMnO3, as well as to extract experimental information concerning the type of orbital order in LaMnO3. This study identifies the lowest-energy optical transition at similar to 2 eV as an intersite d-d transition whose energy is substantially reduced compared to that obtained from the bare intra-atomic Coulomb interaction.