1209.2580 (Motohiko Ezawa)

Hexagonally Warped Dirac Cones and Topological Phase Transition in
Silicene Superstructure    [PDF]

Motohiko Ezawa

Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice. We investigate electronic properties of the (4$\times $4) superstructure, which is formed on top of the Ag(111) substrate. The band structure is obtained by folding that of silicene according to the superstructure. It is a peculiar feature that the two inequivalent K and K' points in the silicene Brillouin zone are identified by the folding. Consequently, two Dirac cones coexist at the same Dirac point in the momentum space. They are hexagonally warped by the Coulomb interaction. The silicene superstructure is a quantum spin-Hall insulator. It is surprising that the band gap never closes even if we apply the electric field. It is highly contrasted to the case of free-standing silicene, where a topological phase transition occurs. We then study generic superstructure and derive the conditions when the K and K' points are identified and when a topological phase transition may occur.

View original: http://arxiv.org/abs/1209.2580