Electronic structure of La1-xSrxMnO3 studied by photoemission and x-ray-absorption spectroscopy

The electronic structure of La1-xSrxMnO3 has been studied by photoemission and O 1s x-ray-absorption spectroscopy. Spectra of the Mn 2p core levels and the valence bands for LaMnO3 and SrMnO3 have been analyzed using a configuration-interaction cluster model. The ground state of LaMnO3 is found to be mixed d4 and d5L states and that of SrMnO3 to be heavily mixed d3 and d4L states, reflecting their strong covalency. The character of the band gap of LaMnO3 is of the p-to-d charge-transfer type while that of SrMnO3 has considerable p-p character as well as p-d character. Holes doped into LaMnO3 mainly of oxygen p character are coupled antiferromagnetically with the d4 local moments of the Mn3+ ions and become itinerant, thus aligning the Mn moments ferromagnetically. The changes in the electronic structure with carrier doping are not of the rigid band type: By La substitution for SrMnO3, the so-called in-gap spectral weight (of eg symmetry) appears with its peak located 1-2 eV below the Fermi level and grows in intensity with increasing La concentration, while the spectral intensity of the eg states above the Fermi level decreases, showing a transfer of spectral weight from the unoccupied to the occupied eg states with electron doping. Meanwhile, the intensity at the Fermi level remains low even in the metallic phase (0.2x0.6). The energy shifts of core-level peaks and valence-band features with x suggest a downward shift of the Fermi level with hole doping, but the shift is found to be very small in the metallic phase. The importance of the orbital degeneracy of the eg band and possible orbital fluctuations in the ferromagnetic phase are pointed out.