Abstract
The interplay between topology and crystalline symmetries in materials can lead to a variety of topological crystalline insulator (TCI) states. Despite significant effort towards their experimental realization, so far only has been confirmed as a mirror-symmetry-protected TCI. Here, based on first-principles calculations combined with a symmetry analysis, we identify a rotational-symmetry-protected TCI state in the transition metal dipnictide family, where or Nb and , As, or Sb. Taking as an exemplar system, we show that its low-energy band structure consists of two types of bulk nodal lines in the absence of spin-orbit coupling (SOC) effects. Turning on the SOC opens a continuous band gap in the energy spectrum and drives the system into a -symmetry-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 . Interestingly, the Dirac cones have tilted energy dispersion, realizing a type-II Dirac fermion state in a topological crystalline insulator. Our results thus indicate that the materials family provides an ideal setting for exploring the unique physics associated with type-II Dirac fermions in rotational-symmetry-protected TCIs.
- Received 10 August 2019
DOI:https://doi.org/10.1103/PhysRevB.100.205118
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