Electronic structure of Mott-Hubbard-type transition-metal oxides

Oxides of Ti and V belong to the Mott-Hubbard regime of the Zaanen-Sawatzky-Allen classification scheme of transition-metal compounds and have simple electronic structures which allow us to study the effect of electron correlation in a transparent way. In this article, we make an overview of our recent photoemission studies on Ti and V oxides. with special emphasis on metal-insulator transitions induced by the control of the width and the filling of the Ti and V 3d bands. Spectroscopic data yield spectral weight transfer between the coherent and incoherent parts of the d band, the spectral intensities at the Fermi level and the chemical potential shifts as functions of band filling. We show that such spectroscopic information well corresponds to the thermodynamic and transport properties and is necessary to understand electron correlation phenomena from a fundamental viewpoint. (C) 2001 Elsevier Science B.V. All rights reserved.