Emergence of Strain Induced Two Dimensional Metallic State in ReS2

We present a highly versatile system ReS2, which transforms from a semiconductor to a two dimensional metal under uni-axial compressive strain along ‘a’ direction in both bulk and monolayer. The 2D nature is realised from highly flat Fermi surfaces and anisotropic transport properties. Moreover the layer independent electronic structure properties are revisited and thermoelectric properties of ReS2 in bulk, monolayer and bilayer forms reveal the competing thermoelectric (TE) coefficients in each form. The in-plane power-factor shows an enhancement over ‘c’-axis value as a function of strain, which is almost two orders of magnitude. In addition, strain induced tunable in-plane anisotropy of almost one order has been observed in both bulk and monolayer ReS2 (around 20%), which further open up the possibility of TE application as nanowires. Our analysis unveils a wide range of application for ReS2 in the field of thermoelectrics as bulk and thin films for a large temperature range. The magnitude of TE coefficients are comparable with other well established transition metal dichalocogenides.