Infrared study of the pressure-induced isostructural metallic transition in Mo${}_{0:5}$W${}_{0:5}$S${}_2$

Abstract

Ternary compounds of Transition Metal Dichalcogenides are emerging as an interesting class of crystals with tunable electronic properties, which make them attractive for nano-electronic and optoelectronic applications. Among them, Mo${}_x$W${}_{1-x}$S${}_2$ is one of the most studied alloys, due to the well-known, remarkable features of its binary constituents, MoS${}_2$ and WS${}_2$. The band-gap of this compound can be modelled varying Mo and W percentages in the sample, and its vibrational modes result from a combination of MoS${}_2$ and WS${}_2$ phonons. In this work, we report transmission measurements on a Mo${}_{0:5}$W${}_{0:5}$S${}_2$ single crystal in the far-infrared range. Absorbance spectra collected at ambient conditions enabled, for the first time, a classification of the infrared-active phonons, complementary to Raman studies. High-pressure measurements allowed to study the evolution of both the lattice dynamics and the free carrier density up to 31 GPa, indicating the occurrence of an isostructural semiconductor-to-metal transition above 18 GPa.

arXiv comment15 pages, 4 figures

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