Superconductivity in Nb5Ir3N: a nitrogen-filled electride

Abstract The hexagonal Mn 5 Si 3 -type compounds possess the capability to accommodate specific atoms in the interstices, thereby creating filled Mn 5 Si 3 -type structures. In Nb-based Mn 5 Si 3 -type system, interstitial atoms like carbon (C) or oxygen (O) have been identified to induce or enhance superconductivity. However, the compounds filled with nitrogen (N) are scarce, and the existence of a N-filled superconductor remains unknown. Here, we report the discovery of a novel ternary nitride superconductor, Nb 5 Ir 3 N, synthesized via incorporating N into the electride Nb 5 Ir 3 . The crystal structure of Nb 5 Ir 3 N conforms to the filled Mn 5 Si 3 -type, belonging to the P 6 3 / mcm space group (No. 193), with cell parameters a = b = 7.8398(2) Å and c = 5.1108(1) Å. Electrical resistivity and magnetic susceptibility demonstrate that Nb 5 Ir 3 N is a type-II superconductor with a T c of 8.7 K. The estimated lower and upper critical fields are 11.0 mT and 12.16 T, respectively. Moreover, specific heat measurements confirm the bulk superconductivity with enhanced electron–phonon coupling in Nb 5 Ir 3 N, as demonstrated by the normalized specific heat jump Δ C e / γT c ∼ 1.59. First-principles calculations emphasize the strong spin–orbit coupling in Nb 5 Ir 3 N.