Semiconductor-Metal Transition in Intermediate-Valence Tm Compounds: Novel Features

Abstract

Tm${\mathrm{Se}}_{0.32}$ ${\mathrm{Te}}_{0.68}$ undergoes a continuous pressure-induced semiconductor-to-metal transition (at 1.4 GPa) in which the Tm ions change their valence. This has been studied by electrical-resistivity, Hall-effect, volume, elastic-constant, and magnetic-susceptibility measurements under pressure. Already in the semiconducting phase all the lattice-related properties indicate strong valence mixing, whereas the magnetic susceptibility remains typical of pure divalent Tm. These new results are discussed in terms of the pressure-induced $4f-5d$ hybridization and local correlation effects.