Semiconductor-topological insulator transition of two-dimensional SbAs induced by biaxial tensile strain

A stibarsen [derived from Latin stibium (antimony) and arsenic] or allemontite, is a natural form of arsenic antimonide (SbAs) with the same layered structure as arsenic and antimony. Thus, exploring the two-dimensional SbAs nanosheets is of great importance to gain insights into the properties of group V-V compounds at the atomic scale. Here, we propose a class of two-dimensional V-V honeycomb binary compounds, SbAs monolayers, which can be tuned from semiconductor to topological insulator. By ab initio density functional theory, both alpha-SbAs and gamma-SbAs display a significant direct band gap, while others are indirect semiconductors. Interestingly, in an atomically thin beta-SbAs polymorph, spin-orbital coupling is significant, which reduces its band gap by 200 meV. Especially under biaxial tensile strain, the gap of a- SbAs can be closed and reopened with concomitant change of band shapes, which is reminiscent of band inversion known in many topological insulators. In addition, we find that the Z(2) topological invariant is 1 for beta-SbAs under the tensile strain of 12%, and the nontrivial topological feature of a- SbAs is also confirmed by the gapless edge states which cross linearly at the Gamma point. These ultrathin group-V-V semiconductors with outstanding properties are highly favorable for applications in alternative optoelectronic and quantum spin Hall devices.