Family of binary transition metal pnictide superconductors

Superconductivity in transition metal nitrides (TMNs) has been investigated for a long time, such as zirconium nitride (ZrN) with a superconducting transition temperature Tc of 10 K. Recently, a phase diagram has been revealed in ZrNx with different nitrogen concentrations, which is very similar to that of high-temperature copper oxide superconductors. Here, we study the TMNs with a face-centered cubic lattice where ZrN and HfN have been experimentally obtained and predict eight new stable superconductors by the first-principles calculations. We find that CuN has a high Tc of 30 K with a very strong electron-phonon coupling (EPC) strength. In contrast to ZrN, CuN has softening acoustic phonons at the high-symmetry point L, which accounts for its much stronger EPC. In addition, the highly symmetrical structure leads to topological nodal points and lines, such as the hourglass Weyl loop on the kx/y/z=0 plane and Weyl points on the kx/y/z=2π/a plane, as well as quadratic band touch at the Γ point. CuN could be a topological superconductor. Our results expand the transition metal nitrides superconductor family and would be helpful to guide the search for high-temperature topological superconductors.