Orbital excitations in LaMnO studied by resonant inelastic X-ray scattering

Inami, Toshiya; Fukuda, Tatsuo  ; Mizuki, Junichiro; Ishihara, Sumio*; Kondo, Hiroshi*; Nakao, Hironori*; Matsumura, Takeshi*; Hirota, Kazuma*; Murakami, Yoichi*; Maekawa, Sadamichi*; Endo, Yasuo*

We report resonant inelastic x-ray scattering experiments of the orbitally ordered manganite LaMnO. When incident photon energy is tuned near the Mn absorption edge, the spectra reveal three features at 2.5 eV, 8 eV and 11 eV. The 8 eV and 11 eV peaks are ascribed to transitions from the O 2 bands to the empty Mn 3 and / bands, respectively. On the other hand, the 2.5 eV peak is considered an orbital excitation across the Mott gap, an electron excitation from the effective lower Hubbard band with the and orbital characters to the upper Hubbard band with the and 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.