Electronic excitations in hole-doped La1-xSrxMnO3 studied by resonant inelastic X-ray scattering

We report a resonant inelastic X-ray scattering (RIXS) study on perovskite manganese oxides La1-xSrMnO3 (x=0, 0.2, and 0.4) at Mn K-absorption edge. Hole-doping effect on the electronic excitations in the strongly correlated electron systems is elucidated by comparing with undoped LaMnO3. The scattering spectra of metallic La0.6Sr0.4MnO3 show that a salient peak appears in low energies indicating the persistence of the Mott gap. At the same time, the energy gap is partly filled by doping holes and the spectral weight shifts toward lower energies. Though the peak position of the excitations shows weak dispersion in momentum dependence, RIXS intensity changes as a function of the scattering angle (2 theta), which is related to the anisotropy. Furthermore, anisotropic temperature dependence is observed in La0.8Sr0.2MnO3 which shows a metal-insulator transition associated with a ferromagnetic transition. We consider that the anisotropy in the RIXS spectra is possibly attributed to the correlation of the orbital degrees of freedom. The anisotropy is large in LaMnO3 with long-range orbital order, while it is small but finite in hole-doped La1-xSrxMnO3 which indicates persistence of short-range orbital correlation. (c) 2005 Published by Elsevier Ltd.