Hole-doping-induced changes in the electronic structure of La _1-xSr _x-FeO ₃: Soft x-ray photoemission and absorption study of epitaxial thin films

We have studied the electronic structure of epitaxially grown thin films of La _1-xSr _xFeO ₃ by in situ photoemission spectroscopy (PES) and x-ray-absorption spectroscopy (XAS) measurements. The Fe 2p and valence-band PES spectra and the O 1s XAS spectra of LaFeO ₃ have been successfully reproduced by configuration-interaction cluster-model calculation and, except for the satellite structure, by band-structure calculation. From the shift of the binding energies of core levels, the chemical potential was found to be shifted downward as x was increased. Among the three peaks in the valence-band spectra of La _1-xSr _xFeO ₃, the peak nearest to the Fermi level (E _F), due to the "e _g band," was found to move toward E _F and became weaker as x was increased, whereas the intensity of the peak just above E _F in the O 1s XAS spectra increased with x. The gap at E _F was seen for all values of x. These results indicate that changes in the spectral line shape around E _F are dominated by spectral weight transfer from below to above EF across the gap and are therefore highly nonrigid-bandlike changes.