Superconductivity with Topological Non-trivial Surface States in NbC

Quantum materials with non-trivial band topology and bulk superconductivity are considered superior materials to realize topological superconductivity. In this regard, we report detailed density functional theory (DFT) calculations and Z2 invariants for the NbC superconductor, exhibiting its band structure to be topologically non-trivial. Bulk superconductivity at 8.9 K is confirmed through DC magnetization measurements under field cooled (FC) and zero field cooled (ZFC) protocols. This superconductivity is found to be of type II nature as revealed by isothermal M-H measurements, and thus the Ginzburg–Landau parameter is calculated. A large intermediate state is evident from the phase diagram, showing NbC to be a strong type-II superconductor. Compared with earlier reports on superconducting NbC, a non-monotonic relationship of critical temperature with lattice parameters is seen. In conclusion, NbC is a type-II around 10 K superconductor with topological non-trivial surface states.