Superconductivity in Intermetallic W7Re13X (X=B and C) Compounds

We discovered superconductivity in W 7 Re 13 X (X=B and C) ( T c =7.1 K and 7.3 K, respectively), and their superconducting properties are discussed. The crystal structure of W 7 Re 13 X is β-Mn-type (cubic, space group: P 4 1 32), and Re atoms form a tilted octahedron. The magnetization ( M – H ) curves show typical type-II superconducting behavior, and the lower critical field H c1 (0), the upper critical field H c2 (0) and the Ginzburg–Landau (GL) parameter κ are 7.7 mT, 11.4 T and 54 for X=B and 4.0 mT, 12.6 T and 80 for X=C, respectively. From the specific heat measurement, the superconducting gap magnitudes are estimated to be 2Δ/ k B T c =4.28 and 4.02, respectively.