Electronic structure of metallic oxides: Band-gap closure and valence control

Abstract

We present an overview of photoemission and x-ray absorption studies on the electronic structure of 3d transition-metal and Bi oxides which show metal-insulator transitions as functions of chemical composition. First, chemical methods of controlling the band gaps and the cation valences are systematically reviewed. Then, the evolution of the single-particle spectral function is demonstrated across the metal-insulator transitions arising from the closing of the band gaps and those due to carrier doping.