Valley Polarization in Two-Dimensional Transition Metal Dichalcogenides Heterostructures with Ferromagnetic Semiconductor

Lifted valleys' degeneracy is a crucial precondition for manipulating valley degrees of freedom and storing information in future spintronics. It was revealed that the Zeeman valley splitting (~0.2 meV/T) could be obtained by applying an external magnetic field, however, this is considered as an inefficient approach. Magnetic proximity effect has been demonstrated to be an effective way to realize exchange interactions, especially in the form of two-dimensional (2D) van der Waals (vdW) heterostructures. We have explored electronic properties of 2D vdW heterostructures using first-principles calculations. It is found that valley splittings of 2 meV and 1.6 meV are achieved in WSe₂/CrI₃ and MoSe₂/CrI₃ heterostructures due to the coexistence of inversion symmetry and time-reversal symmetry breaking. These values correspond to an effective exchange field of ~10 and 8 T, respectively. We also observe that the magnitude of the valley splitting is sensitive to the stacking pattern of the heterostructures. Moreover, the valley splittings and polarization at K and K′ point are switchable through vertical flipping of the CrI₃ magnetization.