Controllable Valley Polarization and Strain Modulation in 2D 2H-VS/CuInPSe Heterostructures.

Two-dimensional (2D) transition metal dichalcogenides endow individually addressable valleys in momentum space at the K and K' points in the first Brillouin zone due to the breaking of inversion symmetry and the effect of spin-orbit coupling. However, the application of 2H-VS monolayer in valleytronics is limited due to the valence band maximum (VBM) located at the Γ point. Here, by involving the 2D ferroelectric (FE) CuInPSe (CIPSe), the ferrovalley polarization, electronic structure, and magnetic properties of 2D 2H-VS/CIPSe heterostructures with different stacking patterns and FE polarizations have been investigated by using first-principles calculations. It is found that, for the energetically favorable AB-stacking pattern, the valley polarization is preserved when the FE polarization of CIPSe is upwards (CIPSe↑) or downwards (CIPSe↓) with the splitting energies slightly larger or smaller compared with that of the pure 2H-VS. It is intriguing that, for the FE CIPSe↑ case, the VBM is expected to pass through the Fermi energy level, which can be eventually achieved by applying biaxial strain and thus the valleytronic nature is turned off; however, for the CIPSe↓ situation, the heterostructure basically remains semiconducting even under biaxial strains. Therefore, with the influence of proper strains, the FE polar reversal of CIPSe can be used as a switchable on/off to regulate the valley polarization in VS. These results not only demonstrate that 2H-VS/CIPSe heterostructures are promising potential candidates in valleytronics, but also shed some light on developing practical applications of valleytronic technology.