Valence Mixing and Semiconductor-Metal Transition in the Sm Monochalcogenides

Abstract

Sm ions in "chemically collapsed" phases of SmS, e.g., ${\mathrm{Sm}}_{0.85}$${\mathrm{Th}}_{0.15}$S and ${\mathrm{Sm}}_{0.82}$${\mathrm{Gd}}_{0.18}$S, are found to be in the state of interconfiguration fluctuations. In contrast, valence fluctuations in pure SmS are shown to be not larger than 3%. Conduction-electron screening does not drastically affect either the location or the effective intra-atomic Coulomb interaction ${U}_{\mathrm{eff}}$ of $4f$ levels in photoemission spectra.