Tunable topological electronic structure of silicene on semiconducting Bi/Si(111)-root3xroot3 substrate: a first-principles

Using first-principles calculations to obtain the crystal and electronic structures, we show that the 1x1 phase of silicene is energetically more favorable than the root3xroot3 silicene superstructure on a semiconducting Bi/Si(111)- root3xroot3 substrate. The band gap of the system is found to be influenced strongly through the participation of Bi-orbitals, which possess a larger spin-orbit coupling strength compared to Si. In particular, the non-trivial (topological) band gap of a few meV in freestanding 1x1 silicene enlarges to 150 meV and becomes trivial in the presence of the substrate. We further show how an out-of-the-plane external electric field can be used to tune the band gap and restore the non-trivial topological phase.