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 ${T}_c$ of 10 K. Recently, a phase diagram has been revealed in ${\mathrm{ZrN}}_x$ 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 ${T}_c$ 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 ${k}_x/y/z=0$ plane and Weyl points on the ${k}_x/y/z=2\ensuremath{\pi}/a$ plane, as well as quadratic band touch at the $\mathrm{\ensuremath{\Gamma}}$ 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.