Tunable ferrovalley semiconductors of Janus VSeCl and VSeBr

Abstract

2D ferrovalley semiconductors have attracted extensive interest due to their valley degree of freedom used for encoding, storing, and manipulating information. To achieve large valley polarization and high Curie temperature in ferrovalley semiconductors, based on the experimental VSe2, we propose Janus VSeCl and VSeBr monolayers and use first-principles calculations to investigate the magnetic and valley properties as well as the strain and carrier doping effects. It is found that both monolayers are dynamically and thermally stable, indicating the experimental feasibility likewise the parent VSe2. Both VSeCl and VSeBr are ferrovalley semiconductors with valley polarizations of 68.3 and 65.1 meV and Curie temperatures of 76 and 106 K, respectively. The compressive strain and hole doping can increase the valley polarization (up to 71.1 meV for VSeCl) due to the enhanced spin-orbit coupling, while the tensile strain and electron doping increase the Curie temperature (up to 218 K) due to the enhanced ferromagnetic super-exchange interaction. The hole doping induces the transition of magnetic easy axis from in-plane to out-of-plane, which is dominated by (dxy/dx2-y2) orbitals of V atoms and (px/py) orbitals of Se atoms. These tunable magnetic and valley properties by strain and carrier doping make Janus VSeCl and VSeBr promising candidates for spintronic and valleytronic applications.