Robust topological insulating property in C₂X-functionalized III-V monolayers

Two-dimensional topological insulators (TIs) show great potential applications in low-power quantum computing and spintronics due to the spin-polarized gapless edge states. However, the small bandgap limits their room-temperature applications. Based on first-principles calculations, a series of C₂X (X = H, F, Cl, Br and I) functionalized III-V monolayers are investigated. The nontrivial bandgaps of GaBi-(C₂X)₂, InBi-(C₂X)₂, TlBi-(C₂X)₂and TlSb-(C₂X)₂are found to between 0.223 and 0.807 eV. For GaBi-(C₂X)₂and InBi-(C₂X)₂, the topological insulating properties originate from thes-px,yband inversion induced by the spin-orbital coupling (SOC) effect. While for TlBi-(C₂X)₂and TlSb-(C₂X)₂, the topological insulating properties are attributed to the SOC effect-induced band splitting. The robust topological characteristics are further confirmed by topological invariantsZ₂and the test under biaxial strain. Finally, two ideal substrates are predicted to promote the applications of these TIs. These findings indicate that GaBi-(C₂X)₂, InBi-(C₂X)₂, TlBi-(C₂X)₂and TlSb-(C₂X)₂monolayers are good candidates for the fabrication of spintronic devices.