Robust two-dimensional topological insulators in derivatives of group-VA oxides with large band gap: Tunable quantum spin Hall states

Recently, group-VA 2D materials have attracted intense attention due to excellent properties in various aspects. Particularly, the strong spin-orbital coupling effect is a remarkable virtue of group-VA 2D materials, which is more widely concerned by researchers. Here, based on first-principles calculations, we provide a systematical investigation on the electronic and topological properties of a novel series 2D compound VA(2) OX (VA = Bi, Sb, As, P; X= S, Se, Te). Combining with the nontrivial Z(2)-type topological invariants, it is confirmed that VA(2) OX 2D crystals possess topologically nontrivial characteristics. The 2D TIs VA(2) OX demonstrate large and tunable nontrivial energy gaps, from 0 to 592 meV, indicating that the tunable QSH effect can be realized at room temperature. Moreover, as an example of VA(2) OX systems, the band gap of Bi-2 OS 2D crystal almost remains unchanged when tensile strain not larger than 8%. Notably, under a large range of strain (+/- 10%), Bi-2 OS keeps the inversion-asymmetric topological insulator phases, which emerges the robustness of nontrivial topology against mechanical deformation and makes it competent for realizing new topological phenomena. The above results are expected to promote further experimental investigation for fundamental exploration and practical application, which will significantly broaden the scientific and technological impact of the QSH effect. (C) 2019 Elsevier Ltd. All rights reserved.