Compressive strain-induced enhancement in valley polarization in β-phosphorene like SnS monolayers

Abstract

Berry curvature (BC), the effective magnetic field in k space, determines the valley Hall effect. Although BC is specific to material, its tunability will provide greater control over this valley polarization. The elasticity in β-phosphorene like 2D SnS monolayer offers ample room for manipulating its electronic properties and BC via mechanical strain. In DFT calculations, SnS monolayer shows a band gap of 2.32 eV, a valley spin splitting (VSS) of 23.8 meV and 140.4 meV, respectively, at K/K’ point on the top (bottom) of the valence (conduction) band. 2.3 % biaxial compressive strain, realizable in experiments, shifts the conduction band minimum (CBM), maximum BC and VSS to the K/K’ point. These features are retained at higher compressive strain. The BC undergoes further enhancement to ∼ 5 Å2 upon continued biaxial compression. The out-of-plane built-in electric field and polarization intrinsically arising from the buckled structure of SnS monolayers is favourably enhanced via in-plane compressive strain, which helps to extend the lifetime of valley polarized excitons. The trend in BC of MX (M = Ge, Sn; X = S, Se, Te) monolayers has been studied. This group of hexagonal buckled monochalcogenide monolayers can pave a new way forward for valleytronics.