Dual topology in van der Waals-type superconductor Nb 2 S 2 C

Nb 2 S 2 C is a van der Waals type layered superconductor with a transition temperature T c = 7.6 K. In this paper, detailed calculations of the electronic structure and topological properties of Nb 2 S 2 C were performed from first principles. We find that Nb 2 S 2 C is a highly anisotropic metal with multi-band characteristics. In the absence of spin–orbit coupling (SOC), there appears one pair of triply degenerate points created by band inversion along the Γ–A line. When SOC is considered, the triple points are gapped. Intriguingly, two distinct types of topological states, including topological Dirac semimetal and topological insulator states, co-emergence in the vicinity of Fermi level. Moreover, the topology of Nb 2 S 2 C is robust to external pressure and the Fermi level can be shifted downward to the topological Dirac semimetal state and topological insulator state at 10 GPa and 14 GPa, respectively. The results herein provide a new platform not only for the studies of physics of low-dimensional superconductor but also for further investigations of topological superconductivity.