Fig. 1: Monolayer ReS₂.

a Crystal structure, composed of 4 rhenium atoms and 8 sulfur atoms in a distorted octohedral structure. The unit cell is delimited by the parallelogram. b–d Band structure of the monolayer along (a) θ = 0^∘, (b) θ = 60^∘ and (c) θ = 120^∘ (see panel a for definition of θ). Circular markers across the bands in panels b–d highlight vertical transitions resonant with the 11th harmonic (H11). Monolayer and bulk (see, e.g., references^30,31) forms of ReS₂ are both inversion symmetric and display a very similar electronic band structure, with a nearly identical direct band gap of 1.4 eV at the Γ point^30,31.