Electronic structure of LaNiO3-x:: An in situ soft x-ray photoemission and absorption study

We study the electronic structure of LaNiO3-x thin films using in situ soft x-ray photoemission and absorption spectroscopy. The in situ high-resolution measurements reveal that states at and near the Fermi level (E-F) in the occupied and unoccupied densities of states are very sensitive to the oxygen content and are directly related to a metal-insulator transition. The highest quality epitaxial films of LaNiO3 show a temperature-dependent sharp peak at E-F. A detailed analysis of its electrical resistivity confirms a T-1.5 behavior over a large temperature range, which has been observed in earlier studies. Local density approximation band structure calculations indicate that the narrowing of the Ni d e(g) electron derived peak at E-F cannot be reproduced by a strained crystal structure, suggesting a renormalization of electronic states at E-F in LaNiO3. The T-dependent spectral changes at E-F, coupled with the resistivity behavior and proximity to a metal-insulator transition, suggest the role of electron correlations in LaNiO3.