Mo 3 ReRuC: A Noncentrosymmetric Superconductor Formed in the MoReRu-Mo 2 C System.

A quaternary compound with the composition Mo 3 ReRuC is obtained in a previously unexplored MoReRu-Mo 2 C system. According to X-ray structural analysis, Mo 3 ReRuC crystallizes in the noncentrosymmetric space group P 4 1 32 [cubic β-Mn-type structure, a = 6.8107(1) Å]. Below 7.7 K, Mo 3 ReRuC becomes a bulk type-II superconductor with an upper critical field close to the Pauli paramagnetic limit. The specific heat data give a large normalized jump Δ C p /γ T c = 2.3 at T c , which points to a strongly coupled superconducting state. First-principles calculations show that its electronic states at the Fermi level are mainly contributed by Mo, Re, and Ru atoms and strongly increased by the spin-orbit coupling. Our finding suggests that the intermediate phase between alloys and carbides may be a good place to look for β-Mn-type noncentrosymmetric superconductors.