Metal to insulator quantum-phase transition in few-layered ReS${}_2$

Abstract

In ReS${}_2$ a layer-independent direct band-gap of 1.5 eV implies a potential for its use in optoelectronic applications. ReS${}_2$ crystallizes in the 1T${}^{\prime }$-structure which leads to anisotropic physical properties and whose concomitant electronic structure might host a non-trivial topology. Here, we report an overall evaluation of the anisotropic Raman response and the transport properties of few-layered ReS${}_2$ field-effect transistors. We find that ReS${}_2$ exfoliated on SiO${}_2$ behaves as an $n$-type semiconductor with an intrinsic carrier mobility surpassing $\hat{I}{¼}_i$ ~30 cm${}^2$/Vs at $T=300$ K which increases up to ~350 cm${}^2$/Vs at 2 K. Semiconducting behavior is observed at low electron densities $n$, but at high values of n the resistivity decreases by a factor > 7 upon cooling to 2 K and displays a metallic $T^2$-dependence. This indicates that the band structure of 1T${}^{\prime }$-ReS${}_2$ is quite susceptible to an electric field applied perpendicularly to the layers. The electric-field induced metallic state observed in transition metal dichalcogenides was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of $T$ and $n$, we find that the metallic state of ReS${}_2$ results from a second-order metal to insulator transition driven by electronic correlations. This gate-induced metallic state offers an alternative to phase engineering for producing ohmic contacts and metallic interconnects in devices based on transition metal dichalcogenides.

25 pages, 5 figures