Combining photoemission and optical spectroscopies for reliable valence determination in YbS and Yb metal

TL;DR

This study combines photoemission and optical spectroscopy to accurately determine the valence state of ytterbium in YbS and Yb metal, effectively distinguishing between different electronic configurations.

Contribution

It introduces a reliable method that integrates photoemission and optical data to precisely identify the valence state in f-electron systems, improving upon previous techniques.

Findings

Yb in YbS and Yb metal is predominantly divalent.

Surface of YbS shows deviation from bulk valence.

The combined method effectively distinguishes energy loss satellites from multiplet peaks.

Abstract

Hard x-ray photoemission and optical spectroscopies have been performed on YbS and Yb metal to determine the precise $f$-electron occupation. A comparison of the photoemission spectra with the energy loss functions in bulk and surface, obtained from optical reflectivity, enables us to distinguish between the energy loss satellite of Yb$^{2+}$ peak and Yb$^{3+}$ multiplet. The results clearly indicate a purely divalent Yb state except for the surface of YbS. We demonstrate that the present method is highly reliable in identifying the electronic structure and the mean valence in $f$-electron systems.