Structural Symmetry, Spin-Orbit Coupling, and Valley-Related Properties of Monolayer WSi2N4 Family.

Recently prepared layered MoSi2N4 exhibits excellent stability and semiconductor properties, adding building blocks for two-dimensional families. In this research, we present the spin-orbit coupling and valley-related properties of monolayer WSi2N4 family. Better than transition metal dichalcogenides, the structural symmetry of WSi2N4 monolayer can be different by changing the stacking of three parts in the monolayers, resulting in a Rashba spin-orbit field. The vertical and horizontal polarization will lift the degeneration of the in-plane and out-of-plane polarized spin, respectively. The gradient of potential energy and the proportion of d orbitals play dominant roles. The in-plane orbitals contribute to the out-of-plane spin polarization, while the out-of-plane orbitals contribute to the in-plane spin polarization. The characteristics of a Rashba semiconductor can be utilized in spin/valley Hall effects, as well as the regulation of the spin direction of the valley electrons, promoting the manipulation of multiple degrees of freedom of electrons in monolayer materials.