BiSbF₂ Monolayer: A 2D Inversion‐Asymmetric Topological Insulator With Linearly Tunable Giant Spin‐Splitting and Bulk Gap

Abstract Using first‐principles calculations, an intriguing 2D topological insulator (TI), fluorinated β‐BiSb monolayer (BiSbF 2 ML) is identified, which not only harbors topologically protected gapless edge states, but also contains spin‐split bulk states with opposite Berry curvature and spin moment in inequivalent valleys. Specifically, its topological edge states reside in a sizable bulk gap of up to 252 meV, sufficiently large for realizing room‐temperature quantum spin Hall effect. For its bulk states, there exist giant spin‐orbit induced spin‐splittings in both the uppermost valence band (390 meV) and the lowermost conduction band (478 meV) due to the breaking of inversion symmetry. In particular, both of the spin‐splitting and the bulk gap can be linearly tuned by external strains from −5% to 5% in a considerable energy window of about 100 meV. Moreover, the intrinsic electronic structure of BiSbF 2 ML near the Fermi level can be well preserved in the substrate‐supported BiSbF 2 ML. The results establish a new 2D inversion asymmetric TI with distinguished bulk state, which provides an ideal platform for exploring the combined effects among spintronics, valleytronics, and topological physics.