Perovskite ThTaN3: A large-thermopower topological crystalline insulator

Abstract

ThTaN3, a rare cubic perovskite nitride semiconductor, has been studied using ab initio methods. Spin-orbit coupling (SOC) results in band inversion and a band gap of 150 meV at the zone center. Despite trivial Z(2) indices, two pairs of spin-polarized surface bands cross the gap near the zone center, indicating that this system is a topological crystalline insulator with the mirror Chern number of |C-m| = 2 protected by the mirror and C-4 rotational symmetries. Additionally, SOC doubles the Seebeck coefficient, leading to a maximum of similar to 400 mu V/K at 150Kfor carrier-doping levels of several 10(17)/cm(3). ThTaN3 combines excellent bulk thermopower with parallel conduction through topological surface states that may point toward newpossibilities for platforms for engineering devices with larger figures of merit.