La${}_{0.65}$Sr${}_{0.35}$MnO${}_{\text{3-}\delta }$ (LSMO) films ($\delta \approx$ 0, 0.07, 0.12) were studied by hard x-ray photoelectron spectroscopy. It is found that the Mn $3d$ valence band states shift to higher binding energies for oxygen-deficient samples, while their overall width decreases as a result of the reduced density of charge carriers. The concurrent disappearance of the well-screened state at the Mn $2p$ level indicates a decrease in hybridization of the Mn $3d$ and the doping-induced states. The lack of clear band gap formation for oxygen-deficient LSMO above the metal/insulator transition is compatible not with polaron formation but, rather, with a Mott variable range hopping mechanism, which is also supported by our transport data. The large electron probing depth of hard x-ray photoelectron spectroscopy is crucial for this study because modifications to the electronic structure may occur in the near-surface region.

• Received 27 June 2012

DOI:https://doi.org/10.1103/PhysRevB.86.155102