materials class

Crystalline symmetries drive a variety of topological crystalline insulator (TCI) phases in materials. Here, based on first-principles calculations combined with associated symmetry analysis, we identify a new rotational-symmetry protected TCI state in the TaAs₂family of compounds. The low-energy band structure consists of two bulk nodal lines in the absence of spin-orbit coupling (SOC) effects. Turning on the SOC opens a continuous band gap in the spectrum and drives the system into a C₂Tsymmetry protected TCI state. On the (010) surface, we show the presence of rotational-symmetry-protected nontrivial Dirac cone states within a local bulk energy gap of 300 meV. Our results indicate that the TaAs₂materials family provides an ideal setting for exploring unique physics associated with the rotational-symmetry protected TCIs.