Spectroscopic Evidence for Localized and Extendedf-Symmetry States in CeO2

Abstract

The occupied and empty electronic states of the insulator Ce${\mathrm{O}}_2$ have been studied by high-energy spectroscopies. The outer-level spectra reveal empty localized $4f^1$ states within the band gap. The core-level spectra display different final-state populations of the $4f$ localized states which are well predicted by a many-body calculation taking into account the presence of $f$-symmetry admixture in the valence band. A mixed valence can be definitely excluded in Ce${\mathrm{O}}_2$.