Quantum spin Hall effect in monolayer and bilayer TaIrTe4

Generally, stacking two quantum spin Hall insulators gives rise to a trivial insulator. Here, based on first-principles electronic structure calculations, we confirm that monolayer TaIrTe4 is a quantum spin Hall insulator and remarkably find that bilayer TaIrTe4 is still a quantum spin Hall insulator. Theoretical analysis indicates that the covalentlike interlayer interaction in combination with the small band gap at the time-reversal invariant Gamma point results in new band inversion in bilayer TaIrTe4, namely, the emergence of quantum spin Hall phase. Meanwhile, a topological phase transition can be observed by increasing the interlayer distance in bilayer TaIrTe4. Considering that bulk TaIrTe4 is a type-II Weyl semimetal, layered TaIrTe4 thus provides an ideal platform to realize different topological phases at different dimensions.