Two-dimensional dual topological insulator in hexagonal IrO

Double topological insulators (DTIs) are systems with two kinds of nontrivial topological indexes. Three-dimensional materials with dual-topological character (DTC) have received extensive research, whereas two-dimensional (2D) DTIs have received less attention. In this paper, we propose a new 2D DTI IrO material by using first-principles calculations. Further calculation reveal it is energetically, dynamically, and mechanically stable. There is a direct band gap in the electronic band structures with and without spin–orbit coupling (SOC), and a SOC-induced band inversion occurs at the M point. Based on the symmetry analysis and the k · p model, the topological invariant Z2 and mirror Chern number C m are determined to be nontrivial. The DTC is supported further by the different behavior of the edge states with and without the mirror symmetry breaking. Our theoretical prediction broadens the domain of candidate 2D DTIs in terms of topological manifestations as well as material realization.