Doping Dependence of the Electronic Structure of Ba_{1-x}K_{x}BiO_{3} Studied by X-Ray Absorption Spectroscopy

摘要

We have performed x-ray absorption spectroscopy (XAS) and x-ray photoemissionspectroscopy (XPS) studies of single crystal Ba_{1-x}K_{x}BiO_{3} (BKBO)covering the whole composition range $0 \leq x \leq 0.60$. Several features inthe oxygen 1\textit{s} core XAS spectra show systematic changes with $x$.Spectral weight around the absorption threshold increases with hole doping andshows a finite jump between $x=0.30$ and 0.40, which signals themetal-insulator transition. We have compared the obtained results withband-structure calculations. Comparison with the XAS results ofBaPb_{1-x}Bi_{x}O_{3} has revealed quite different doping dependences betweenBKBO and BPBO. We have also observed systematic core-level shifts in the XPSspectra as well as in the XAS threshold as functions of $x$, which can beattributed to a chemical potential shift accompanying the hole doping. Theobserved chemical potential shift is found to be slower than that predicted bythe rigid band model based on the band-structure calculations.