Eur. Phys. J. B (2013) 86: 139
https://doi.org/10.1140/epjb/e2013-31029-1

Regular Article

Hexagonally warped Dirac cones and topological phase transition in silicene superstructure

Department of Applied Physics, University of Tokyo, Hongo 7-3-1, 113-8656 Tokyo, Japan

^a e-mail: ezawa@ap.t.u-tokyo.ac.jp

Received: 11 November 2012
Published online: 8 April 2013

Abstract

Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice. We investigate the topological properties of a silicene superstructure generated by an external periodic potential. The superstructure is a quantum spin-Hall (QSH) insulator if it is topologically connected to silicene. It is remarkable that two inequivalent K and K′ points in the silicene Brillouin zone are identified in certain superstructures. In such a case, two Dirac cones coexist at the same Dirac point in the momentum space and they are hexagonally warped by the Coulomb interaction. We carry out a numerical analysis by taking an instance of the (3 × 3) superstructure on the (4 × 4) structure of the Ag substrate. We show that it is a QSH insulator, that there exists no topological phase transition by external electric field, and that the hexagonally warping occurs in the band structure.