Cobalt-Dimer Nitrides: A Potential Novel Family of High-Temperature Superconductors

We predict that the square lattice layer formed by Co_2N_2^2- diamond-like units can host high-temperature superconductivity. The layer appears in the stable ternary cobalt nitride, BaCo_2N_2. The electronic physics of the material stems from Co_2N_2 layers where the dimerized Co pairs form a square lattice. The low energy physics near Fermi energy can be described by an effective two-orbital model. Without considering interlayer couplings, the two orbitals are effectively decoupled. This electronic structure satisfies the “gene” character proposed for unconventional high-temperature superconductors. We predict that the leading superconducting pairing instability is driven from an extended s-wave (s^\pm) to a d-wave by hole doping, e.g., in Ba_1-xK_xCo_2N_2. This study provides a new platform to establish the superconducting mechanism of unconventional high-temperature superconductivity.