Superconductivity in Nb5Ir3N: a nitrogen-filled electride
The hexagonal Mn5Si3-type compounds possess the capability to accommodate specific atoms in the interstices, thereby creating filled Mn5Si3-type structures. In Nb-based Mn5Si3-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, Nb5Ir3N, synthesized via incorporating N into the electride Nb5Ir3. The crystal structure of Nb5Ir3N conforms to the filled Mn5Si3-type, belonging to the P63/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 Nb5Ir3N is a type-II superconductor with a Tc 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 Nb5Ir3N, as demonstrated by the normalized specific heat jump ΔCe/γTc ∼ 1.59. First-principles calculations emphasize the strong spin–orbit coupling in Nb5Ir3N.
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