Spin filter effect of germanene nanoribbon controlled by local exchange field and electric field

Abstract

Germanene, which has been synthesized recently, is a single-layered material composed of germanium atoms. Almost all the striking properties of graphene can be transferred to germanene, because both of them have the same honeycomb lattice structure. In contrast with graphene, germanene has a sizable band gap and spin dependent helical edge states, which make it attractive candidate for spintronic applications. By using the nonequilibrium Green’s function method, the effects of <i>Z</i>-axis local exchange field and electric field on spin-polarized transport properties in germanene nanoribbon are studied theoretically. The results reveal that by exerting an exchange field with a strength greater than twice the effective spin-orbit coupling to the edge region of germanene, the spin resolved band gaps can be generated in different energy ranges, and thus 100% filtering of spin-up or spin-down electrons can be achieved. We theoretically propose a method to reduce the threshold exchange field strength for the spin filter effect by using the electric field. The results show that the spin-filter effect can be achieved in a larger energy range under a weaker exchange field when the electric field are applied to the entire central device region. With the increase of the local exchange field intensity, the energy range corresponding to the spin filter effect will increase significantly.