Non-trivial topological crossover in functionalized AlBi monolayer

The incorporation of spin-orbit coupling and altering the orbital composition close to the Fermi level via functionalization are two essential techniques for exploring topological insulators. We have shown through an ab-initio study that spin-orbit coupling transforms the fluorinated AlBi honeycomb monolayer from a normal insulator to a topological insulator with a large band gap. The combined effects of functionalization and spin-orbit coupling led to a band-inversion in the AlBi honeycomb monolayer. This monolayer has a nontrivial topological character, as confirmed by the reported s/p band inversion in the band structures, the Z2 topological invariant and the clear demonstration of the topological gapless edge states bridging the valence band and conduction band. In addition, it is found that compressing the fluorinated AlBi lattice by about 3 % triggered the topological phase transition, which results in a normal state. The reported nontrivial band gap of 0.36 eV in the fluorinated AlBi monolayer is sufficient to make them a suitable consideration for spintronic devices at room temperature.