Electronic Structure of the Chevrel-Phase Compounds Sn$_{x}$Mo$_{6}$Se$_{7.5}$: Photoemission Spectroscopy and Band-structure Calculations

摘要

We have studied the electronic structure of two Chevrel-phase compounds,Mo$_6$Se$_{7.5}$ and Sn$_{1.2}$Mo$_6$Se$_{7.5}$, by combining photoemissionspectroscopy and band-structure calculations. Core-level spectra taken withx-ray photoemission spectroscopy show systematic core-level shifts, which donot obey a simple rigid-band model. The inverse photoemission spectra imply theexistence of an energy gap located $\sim 1$ eV above the Fermi level, which isa characteristic feature of the electronic structure of the Chevrel compounds.Quantitative comparison between the photoemission spectra and theband-structure calculations have been made. While good agreement between theoryand experiment in the wide energy range was obtained as already reported inprevious studies, we found that the high density of states near the Fermi levelpredicted theoretically due to the Van Hove singularity is considerably reducedin the experimental spectra taken with higher energy resolution than in theprevious reports. Possible origins are proposed to explain this observation.