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

Abstract

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 \ensuremath{\alpha}-SbAs and \ensuremath{\gamma}-SbAs display a significant direct band gap, while others are indirect semiconductors. Interestingly, in an atomically thin \ensuremath{\beta}-SbAs polymorph, spin-orbital coupling is significant, which reduces its band gap by 200 meV. Especially under biaxial tensile strain, the gap of \ensuremath{\beta}-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 \ensuremath{\beta}-SbAs under the tensile strain of 12%, and the nontrivial topological feature of \ensuremath{\beta}-SbAs is also confirmed by the gapless edge states which cross linearly at the \ensuremath{\Gamma} point. These ultrathin group-V-V semiconductors with outstanding properties are highly favorable for applications in alternative optoelectronic and quantum spin Hall devices.