Valley and spin polarization manipulated by electric field in magnetic silicene superlattice

Abstract

Silicene is a close relative of graphene with a honeycomb lattice structure. However, silicene is unlike the strictly two-dimensional graphene and it has a buckled structure, i.e., the A and B atoms form two sublattice planes with a small vertical separation distance in between. Thus a perpendicular electric field applied to silicene can induce a staggered sublattice potential and different onsite energies in the A and B sublattices. As a result, silicene has a large spin-orbit gap compared with graphene. In addition, the mass of Dirac electrons in silicone is controllable by an external electric field, which leads to several controllable polarized transports in the silicene junction, including valley-, spin-and pseudospin-polarization transport. However, in a single silicone junction the manipulations of polarizations are not ideal. In this work, we consider several silicene-based superlattices in order to effectively control the properties of polarization transport. Using the transfer matrix method, we study valley-, spin-and pseudospin-polarization transport in silicene-based electrostatic potential, ferromagnetic and antiferromagnetic superlattices. The effects of ferromagnetic exchange field, antiferromagnetic exchange field and chemical potential on transport properties are analyzed and the roles of electrostatic field in regulating valley-, spin-and pseudospin-polarization are discussed. The ferromagnetic superlattices result in spin-dependent chemical potential in ferromagnetic regime, while Dirac-like mass depends on the antiferromagnetic exchange field and spin. For electrostatic potential superlattice, the pseudospin-polarization occurs and there is no spin-polarixation nor valley-polarization. The peaks of both the pseudospin conductances are completely separated from each other and the pseudospin is completely polarized in the wide range of the zero field for both sides. For ferromagnetic superlattice, the ferromagnetic exchange field and chemical potential lead to the concurrences of spin-and valley-polarizations. The spin-and valley-polarizations can realize a sudden reversal from -1 to +1 by adjusting the electric field. For antiferromagnetic superlattice, the similar properties of spin-and valley-polarizations are observed. Comparing with the ferromagnetic superlattice, only the polarization order is different when the same change is made in the electric field. These results indicate that when the number of lattices in the superlattice is more than 10, the valley-, spin-and pseudospin-polarization reach 100% easily in silicene-based superlattice. The polarization direction can be reversed by adjusting the electric field, which is helpful in manipulating the freedom degrees of valley, spin and pseudospin in silicene superlattice.