Strain-induced topological quantum phase transition in phosphorene oxide

Using {\em ab initio} density functional theory, we investigate the structural stability and electronic properties of phosphorene oxides (PO$_{x}$) with different oxygen compositions {\em x}. A variety of configurations are modeled and optimized geometrically to search for the equilibrium structure for each {\em x} value. Our electronic structure calculations on the equilibrium configuration obtained for each {\em x} reveal that the band gap tends to increase with the oxygen composition of {\em x} < 0.5, and then to decrease with {\em x} > 0.5. We further explore the strain effect on the electronic structure of the fully oxidized phosphorene, PO, with {\em x} = 1. At a particular strain without spin-orbit coupling (SOC) is observed a band gap closure near the ${\Gamma}$ point in the {\em k} space. We further find the strain in tandem with SOC induces an interesting band inversion with a reopened very small band gap (~5 meV), and thus gives rise to a topological quantum phase transition from a normal insulator to a topological insulator. Such a topological phase transition is confirmed by the wave function analysis and the band topology identified by the {\em Z$_{2}$} invariant calculation.