Constructive coupling effect of topological states and topological phase transitions in plumbene

Abstract

Combining tight-binding (TB) models with first-principles calculations, we investigate electronic and topological properties of plumbene. ``Constructive'' coupling effects of topological states are found in the low-buckled plumbene, causing the system being a normal insulator, opposite to topologically nontrivial states formed in other two-dimensional (2D) group IVA monolayers (from graphene to stanene). Local topologic states are found being located not only at the $\mathrm{\ensuremath{\Gamma}}$ point in the Brillouin zone, but also at the $K/{K}^{\ensuremath{'}}$ points, whose coupling determines the final topological behaviors of the whole system. Based on this mechanism, several schemes are raised to produce a globally topological state in the plumbene. When the plumbene is functionalized with ethynyl ($\mathrm{Pb}{\mathrm{C}}_{2}\mathrm{H}$), a quantum spin Hall (QSH) state comes out. Very interestingly, when an exchange field is introduced to the pristine plumbene, the system exhibits a quantum anomalous Hall (QAH) effect despite the coupling effect of the topological states.