Family of binary transition metal pnictide superconductors

TL;DR

This paper predicts eight new stable transition metal nitride superconductors with high transition temperatures and topological features, expanding the family of superconductors and guiding future high-temperature superconductor research.

Contribution

The study introduces eight predicted stable TMN superconductors with high Tc and topological properties, based on first-principle calculations, highlighting CuN's potential as a topological superconductor.

Findings

CuN has a high Tc of 30 K with strong electron-phonon coupling.

CuN exhibits softening acoustic phonons at high symmetry points.

CuN may be a topological superconductor with protected nodal points and lines.

Abstract

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 face-centered cubic lattice, where ZrN and HfN have been experimentally obtained, and predict eight new stable superconductors by the first-principle 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 protected nodal points and lines, such as the hourglass Weyl loop in kx/y/z = 0 plane and Weyl points in kx/y/z = 2{\pi}/a plane, as well as quadratic band touch at {\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.