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.