Correlation effects in the electronic structure and photoemission spectra of mixed-valence cerium compounds

Abstract

The electronic ground states and core-hole and valence-hole excited states of so-called tetravalent and mixed-valence Ce compounds are studied taking into account strong correlations among $4f$ electrons. By an analysis of the core-level photoemission satellites, Ce${\mathrm{O}}_2$, which has been thought to be tetravalent, is identified as a mixed-valence system with $\sim 0.6 4f$ electron, where the magnetic moment of the $4f^1$ configuration is quenched via singlet coupling between the $4f$ electron and the O $2p$ hole. $4f$-derived satellite features in the resonant photoemission spectrum of Ce${\mathrm{O}}_2$ are calculated, which qualitatively explain resonant photoemission spectra of tetravalent Ce intermetallic compounds. The core-level and $4f$-derived photoemission spectra of mixed-valence CeN are also studied by considering only the $4f$-electron—N $2p$-hole coupling as in Ce${\mathrm{O}}_2$ and neglecting the $4f-5d$ mixing. It is also suggested that for the $\alpha$ phase of Ce metal the absence of a localized magnetic moment, volume collapse, and a $4f^0$ signal in the core-level photoemission spectra are explained by this type of configuration-mixing description.