Spin-polarized transport in graphene nanoribbons with Rashba spin-orbit interaction: the effects of spatial symmetry

Topology and applications of 2D Dirac and semi-Dirac materials

Two dimensional (2D) Dirac materials, such as graphene, hold promise of being useful in energy storage, and thus have merged as candidates that are worth exploring through the last couple of decades. In this chapter, we mainly focus on three aspects of these materials, namely, the electronic properties, via computing the band structure, the topological properties through the topological invariants, and the prospects of these 2D materials for spintronic applications, via studying the spin polarized transport. All of these properties are correlated, and hence warrant a thorough discussion. Further, in order to ascertain whether a band deformation induces noticeable effects on the electronic, topological and spintronic properties, we have considered a 2D semi-Dirac system, that does not have Dirac cones, however the conduction and the valence bands touch at an intermediate to the Dirac points in the Brillouin zone. From our studies, we infer that the behaviour of these semi-Dirac systems is quite distinct from their Dirac counterpart. Finally, in order to have noticeable spin polarized transport, we use heavy adatoms (such as, Au) on the graphene matrix which enhances the spin–orbit coupling, and thereby propose a mechanism that will ramify on the spintronic applications.

Three-terminal spin/charge current router

Topological insulator materials have wide applications in electronic and spintronic devices by utilizing the protected edge states. In this paper, based on these topological edge states and energy gaps, we propose some types of spin/charge current router in a three-terminal system consisting of silicene-like nanoribbons (SiNRs). The current is well controlled by the helical edge states of zigzag SiNRs (ZSiNRs) and external fields. Using the tight-binding model and non-equilibrium Green's function theory, we investigate three types of such router. The first type is a spin current shunter which separates the spin-up and spin-down current into different leads. The second type is a spin filter which separates the spin-polarized electrons into one of those leads. The last type is a charge current switcher which switches the charge current from one lead to the other lead. The local current distribution is calculated for the specific electron path. We find that the small Rashba does not destroy the filtering properties of the system. Besides, as an example, we employ the Landauer-Büttiker formula to obtain the current-voltage curves of the first type router and investigate the transmittance reciprocity relations in such a three-terminal system. We believe these proposed spin/charge current routers, which can separate the specific current into the expected lead, have potential applications in the future spintronics designs.