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

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 beta-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 similar to 5 angstrom(2) 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.

Automated summary

Berry curvature, the effective magnetic field in k space, can be controlled through mechanical strain to achieve better control over valley polarization. SnS monolayer shows interesting electronic properties and enhanced Berry curvature under achievable compressive strain, which may extend the lifetime of valley polarized excitons.