2D O-PTl monolayer: a robust large bandgap topological insulator

Searching for ideal two-dimensional (2D) topological insulators (TIs) with large bandgaps is significant for the realization of the quantum spin Hall effect (QSHE) at room temperature. By employing ab initio calculations based on the density functional theory, we predict a novel 2D TI, semi-oxidized phosphorus thallium O-PTl, which harbors a series of excellent properties, such as high flexibility, chemical stability, and a large tunable 2D TI bandgap. In contrast to the monolayer PTl, semi-oxidation on one side of P induces a large TI bandgap of 403 meV, which can be further enlarged to 460 meV by biaxial strain, far exceeding the temperature required for practical application. Due to the semi-oxidation on one side of P, the material is chemically stable against surface oxidization when grown on suitable substrates forming heterostructures. For the O-PTl/BN and O-PTl/graphane heterostructures, we find that the nontrivial topological bandgap of O-PTl is almost not affected by substrate, which is crucial to the experimental realization of QSHE. Our results demonstrate a new type of 2D TI materials and provide a new alternative strategy to devise topological electronic devices operating at room temperature. (paper)