Superconductivity in Intermetallic W7Re13X (<TEX>$\mathrm{X}=\text{B}$</TEX> and C) Compounds

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We discovered superconductivity in W7Re13X (<TEX>$\mathrm{X}=\text{B}$</TEX> and C) (<TEX>$T_{\text{c}} =7.1$</TEX> K and 7.3 K, respectively), and their superconducting properties are discussed. The crystal structure of W7Re13X is <TEX>$\beta$</TEX>-Mn-type (cubic, space group: <TEX>$P4_132$</TEX>), and Re atoms form a tilted octahedron. The magnetization (<TEX>$M$</TEX>–<TEX>$H$</TEX>) curves show typical type-II superconducting behavior, and the lower critical field <TEX>$H_{\text{c1}}(0)$</TEX>, the upper critical field <TEX>$H_{\text{c2}}$</TEX>(0) and the Ginzburg–Landau (GL) parameter <TEX>$\kappa$</TEX> are 7.7 mT, 11.4 T and 54 for <TEX>$\mathrm{X}=\text{B}$</TEX> and 4.0 mT, 12.6 T and 80 for <TEX>$\mathrm{X}=\text{C}$</TEX>, respectively. From the specific heat measurement, the superconducting gap magnitudes are estimated to be <TEX>$2\Delta/k_{\text{B}}T_{\text{c}}=4.28$</TEX> and 4.02, respectively.
2005-02-15