Controllable Valley Polarization and Strain Modulation in 2D 2H-VS2/CuInP2Se6 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-VS2 monolayer in valleytronics is limited due to the valence band maximum (VBM) located at the Gamma point. Here, by involving the 2D ferroelectric (FE) CuInP2Se6 (CIPSe), the ferrovalley polarization, electronic structure, and magnetic properties of 2D 2H-VS2/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 up arrow) or downwards (CIPSe down arrow) with the splitting energies slightly larger or smaller compared with that of the pure 2H-VS2. It is intriguing that, for the FE CIPSe up arrow 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 down arrow 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 VS2. These results not only demonstrate that 2H-VS2/CIPSe heterostructures are promising potential candidates in valleytronics, but also shed some light on developing practical applications of valleytronic technology.