Electronic structure of and the metal-insulator transition in La_1−xSr_xCoO_3−δ: a soft-X-ray absorption study

Abstract

We report the soft-X-ray absorption spectra at the oxygen K-edge of La_1−xSr_xCoO_3−δ (x=0.0, 0.1, 0.2, 0.3 and 0.4) series with experimentally determined δ values. We show that the doping of holes by replacing La³⁺ with Sr²⁺ induces states within the band gap of the insulating undoped compound for small x and these doped states have a very substantial oxygen 2p character. This indicates that the insulating compounds belong to the charge transfer insulator regime. With increasing Sr content, the doped states broaden into a band overlapping the top of the primarily oxygen p-derived band, leading to an insulator-metal transition at x≥0.2.