Strongly distinct electrical response between circular and valley polarization in bilayer transition metal dichalcogenides

Abstract

We introduce a physical model to describe the influence of a perpendicular electric field on circular polarization (CP) and valley polarization (VP) in bilayer transition metal dichalcogenides. Our results uncover that electric-field-dependent CP and VP are quite distinct from each other. The dependence of CP on the electric field harbors a W pattern and possesses the minimum when the potential energy difference between the two layers is equal to the strength of spin-orbit coupling. Such dependence of CP stems from the modulation of energy cost for interlayer hopping and spin-dependent layer polarization. In contrast, VP is strictly absent in primitive bilayers and increases monotonically with increasing strength of electric field, resulting from the continuous variation of valley magnetic moments and inversion-symmetry breaking. Our model elaborates well the recent experimental observations for which the origin is under debate. Moreover, we demonstrate that the manipulation of layer and valley pseudospin is fully tunable by perpendicular electric fields, paving the way for prospects in electrical control of exotic layer-valleytronics.