Electronic structure and spin polarization in Silicene nanostructures

Abstract

Graphene is nowadays a famous material due to its exquisite properties and potential applications. However, silicene is more recent experimentally verified finding which possesses the same main features that make graphene interesting. Additionally silicene has two advantages over graphene. Firstly it has considerably larger band gap which is very important for electronic applications. Secondly silicene is much more suitable when it comes to actual applications with today's silicon-based semiconductor industry. The electronic structure of silicene has been studied with tight-binding method supplemented by Green's function calculations. Concerning bulk silicene, the focus has been on the band gap and its manipulation with electric field. We have also studied nanoribbons where we have looked for localized effects at the edges. Furthermore an artificial interface has been created in the middle of the ribbon by applying opposite electric fields on the separate halves of the nanoribbon. In summary, the results indicate that the band gap of silicene can be externally tuned with electric field. The gap becomes smaller until it completely closes by increasing the field. After this is starts to grow once more. Easy manipulation of the gap suggests a wide range of potential applications in electronics. Nanoribbons exhibit quantum spin hall effect as there exist helical edge states in the bulk gap. In effect this suggests the topologically insulating nature of silicene. Furthermore, electric field interfaced silicene shows localization of states near the interface. These interface states cross the gap and their localization strengthens with increasing electric field. Not much can be said yet as further research is needed in the form of different geometries or application of magnetic field, for example.