Phase transition of Quasi-topological insulator to band insulator in bilayer Germanene

Bilayer germanene nanoribbons (bGNR), due to interlayer bonds and strong spin-orbit coupling, have more application in the design of nano-devices and spintronics. Quantum transport properties and topological phases transition of zigzag superlattice bGNR exposed to the vertical electric field and Rashba spin-orbit coupling (RSOC) are studied within the tight-binding based non-equilibrium Green's function approach. Results demonstrate that by applying the vertical external electric field, a gap opening and metal-semimetal phase transition occur in the system. Meanwhile, we found the topological phase transition of a quasi-topological insulator-band insulator by applying a vertical electric field in bGNR. Further, results reveal that by tuning the RSOC strength, we can control the spin current. This controllability of spin and quantum transport in GNR may contribute to potential applications in nano-devices and the development of spintronic.