Orbital Excitations In Lamno3 Studied By Resonant Inelastic X-Ray Scattering

We report resonant inelastic x-ray scattering experiments of the orbitally ordered manganite LaMnO3. When incident photon energy is tuned near the Mn K absorption edge, the spectra reveal three features at 2.5, 8, and 11 eV. The 8- and 11-eV peaks are ascribed to transitions from the O 2p bands to the empty Mn 3d and 4s/4p bands, respectively. On the other hand, the 2.5-eV peak is considered an orbital excitation across the Mott gap, i.e., an electron excitation from the effective lower Hubbard band with the d(3x2-r2) and d(3y2-r2) orbital characters to the upper Hubbard band with the d(y2-z2) and d(z2-x2) ones. The weak dispersion and characteristic azimuthal angle dependence of this excitation are well reproduced by a theory which includes orbital degeneracy and strong electron correlation.