Tunable light-induced topological edge states in strain engineering of bismuthene monolayers

Abstract

Designing quantum materials on demand is the main goal of modern condensed matter physics. In our work, we investigate Floquet band engineering via the combination of strain effects and periodic light fields in bismuthene, i.e., Bi(110) and Bi(111) monolayers. Bi(110) monolayers are discovered to be elemental ferroelectric semiconductors that can host double pairs of gapless helical edge states. Our work reveals that the double pairs of gapless helical edge states are not robust to edge terminations, and circularly polarized light could drive the double pairs of gapless helical edge states into only one single pair of gapless helical edge states in the Bi(110) monolayer. Moreover, for the Bi(111) monolayer, which shows a Z₂ protected quantum spin Hall effect, light could drive the pair of helical edge states into chiral edge states. However, under different strain effects, the light–bismuthene coupled system could show different Floquet-engineering behaviours. For example, with compressive strain on the Bi(111) monolayer, the light could successively drive the quantum spin Hall effect into a quantum anomalous Hall effect with tunable Chern numbers. Our work demonstrates that Floquet band engineering via periodic light fields could provide a route to manipulate the edge states and topological phase transitions in bismuthene, and the combination of strain effects and periodic light fields could play an important role in designing quantum materials on demand.