Discovery of a new quantum spin Hall phase in bilayer plumbene

Abstract

Two-dimensional (2D) large-gap quantum spin Hall (QSH) insulator are imperative for achieving dissipationless transport devices. The bottleneck preventing applications from QSH phase, however, is lack of feasible 2D films experimentally. By using first-principles calculations, here we propose a new 2D topological phase in the bilayer plumbene. Its geometric stability is confirmed by phonon spectrum simulation and ab initio molecular dynamics simulation. We find that it can turn into a nontrivial QSH phase under tensile strain and its nontrivial gap is highly tunable by external strains. The origin behind QSH effect can be identified by s–px,y band inversion, topological invariant Z2, and helical edge states within the bulk gap. Also, a heterostructure composed of bilayer plumbene deposited on semiconducting MoS2 substrate remains topologically nontrivial properties with a sizable gap. These findings provide a promising platform to design a large-gap QSH insulator in Pb film, which show potential applications in spintronics devices.