A new topological crystalline insulator in two-dimensional PbPo with tunable large bulk gaps

Abstract

On the basis of first principles calculations, we predict that the PbPo monolayer is a new 2D topological crystalline insulator (TCI) with crystalline-protected Dirac states at the edges. This topologically nontrivial phase stems from the strong crystal field effect in the monolayer, which lifts the degeneracy between Po-p_x,y and Pb-p_z orbitals, thus giving rise to a p_x,y–p_z band inversion. As compared to the narrow band gap in bulk PbPo, the quantum confinement of the 2D structure leads to a larger band gap of 364.77 meV, making it viable for the practical realization of the TCI phase at room temperature. Additionally, its band topology is preserved in quantum well formed by sandwiching the PbPo monolayer between NaI layers. This new 2D TCI with a large bulk gap is a potential candidate in future spintronic devices with ultralow dissipation.