Broken cubic symmetry driven co-emergence of type-I and type-II Dirac points in topological crystalline insulator ThTaN3.

ThTaN3 is known as a rare cubic perovskite nitride topological crystalline insulator (TCI). Here, we propose, using first-principles calculations, that compressive uniaxial (0 0 1) strained ThTaN3 can host a three dimensional nodal-chain semimetal state when spin-orbit coupling (SOC) is ignored. When SOC is turned on, the nodal-chain is gapped out, resulting in a pair of type-II Dirac points as protected by C 4 crystal symmetry. Intriguingly, under an increasing compressive uniaxial (0 0 1) strain, a new pair of type-I Dirac points emerges, realizing a novel Dirac semimetal that hosts both type-I and type-II Dirac points in momentum space. The electronic structures of the projected surfaces are also discussed, and the unique Fermi arcs are observed. Our results make ThTaN3 a promising platform for experimental realization of multiple types of Dirac fermions in a single material system.