In-plane polarization induced ferroelectrovalley in a two-dimensional rare-earth halide

Abstract We propose a mechanism where the valley splitting is caused by an in-plane polarization and is therefore coupled with it, making it possible to control the valley degree of freedom electrically. We show, by first-principles calculations, that the Eu ₂ GdCl ₆ monolayer (ML) exhibits an in-plane polarization coupled with a spontaneous valley splitting. Thus, unlike the conventional magnetic field switching of the valley degree of freedom, the valley polarization can be switched by an external electric field. We show that a similar ferroelectric-ferrovalley (FE) coupling is also seen in the previously reported FE (CrBr ₃ ) ₂ Li ML.