Bismuthylene Monolayer: A Promising Quantum Spin Hall Insulator with Large Band Gaps

Abstract: By means of first-principles calculations, we predict a new 2D QSH insulator in the porous allotrope of Bismuth monolayer, bismuthylene, its dynamics stability being confirmed by phonon spectrum and molecular dynamics simulations. The analyses of electronic structures reveal that it is a native QSH state with a gap much as large as 0.29 eV at the {\Gamma} point, which is larger than the buckled (0.2 eV) and flattened (0.2 eV) bismuth, Bi4Br4 (0.18 eV), as well as stanene (0.1 eV), also more stable energetically than these systems. Interestingly, the bismuthylene has tunable band gaps and nontrivial band topology under strains within -6 - 5 % and electric fields up to 0.8 eV/{\AA}. Furthermore, a tight-binding model is constructed to explain the low-energy physics behind band topology induced by spin-orbit coupling. We also propose a quantum well by sandwiching bismuthylene between two BN sheets and reveals that this structure remains topologically nontrivial with a sizeable band gap. This findings on QSH effect of bismuthylene provide a viable platform in new generation of dissipationless electronics and spintronics devices.