Gallium bismuth halide GaBi-X2 (X =I, Br, Cl) monolayers with distorted hexagonal framework: Novel room-temperature quantum spin Hall insulators

摘要

Quantum spin Hall (QSH) insulators with a large topologically nontrivial bulk gap are crucial for future applications of the QSH effect.Among these,group Ⅲ-Ⅴ monolayers and their halides,which have a chair structure (regular hexagonal framework),have been widely studied.Using first-principles calculations,we formulate a new structure model for the functionalized group Ⅲ-Ⅴ monolayers,which consist of rectangular GaBi-X2 (X =I,Br,Cl) monolayers with a distorted hexagonal framework (DHF).These structures have a far lower energy than the GaBi-X2 monolayers with a chair structure.Remarkably,the DHF GaBi-X2 monolayers are all QSH insulators,which exhibit sizeable nontrivial band gaps ranging from 0.17 to 0.39 eV.The band gaps can be widely tuned by applying different spin-orbit coupling strengths,resulting in a distorted Dirac cone.