CuNNi₃: a new nitride superconductor with antiperovskite structure

We have successfully synthesized a new Ni-based antiperovskite nitride, CuNNi 3 , which exhibits superconductivity with a transition temperature T c of 3.2 K. This compound is the second nitride superconductor in the Ni-based antiperovskites. We report the synthesis and physical properties of CuNNi 3 , characterized via x-ray diffraction, magnetization, resistivity, and heat capacity measurements. The temperature dependence of the specific heat is consistent with an isotropic s-wave gap (Δ 0 = 0.42 meV). The estimated electron–phonon coupling strength (λ ep = 0.53) suggests that the superconductivity in CuNNi 3 is induced by electron–phonon coupling, and the gap ratio (2Δ 0 / k B T c ) of 3.05 indicates that it is a weak coupling superconductor. Furthermore, the relatively high Ginzburg–Landau parameter (κ = 24.6) signifies that CuNNi 3 is a type II superconductor.