Superconductivity in ternary borides MReB (M = Mo, W) with the CuAl2-type structure.

We report the structural and superconducting properties of ternary transition metal borides MoReB and WReB. Both compounds crystallize in the tetragonal CuAl 2 -type structure, in which the Re and Mo/W atoms share the same crystallographic site and form one-dimensional zigzag chains along the c -axis. The results of resistivity, magnetic susceptibility, and specific heat measurements indicate that these borides are weakly coupled, fully gapped, type-II superconductors. The superconducting transition temperature T c , upper critical field, and Ginzburg-Laudau parameter are determined to be 5.25 K, 2.1 T, 15.6 for MoReB, and 5.30 K, 2.0 T, 15.7 for WReB. Despite their nearly identical T c values, the Sommerfeld coefficient of WReB is more than 20% smaller than that of MoReB, suggesting that the electronic density of states at the Fermi level is not the dominant factor in determining T c. In addition, the upper critical fields of both MoReB and WReB exhibit an anomalous linear temperature dependence and possible origins are discussed. • In both MoReB and WReB, the Mo/W and Re atoms share the same crystallographic site. • Both borides are found to be weakly coupled, fully gapped, type-II superconductors. • T c of these borides is not determined primarily by the density of states at the Fermi level. • A linear temperature dependence of upper critical field is observed in both cases, ascribing to Fermi surface anisotropy or multiband effects. [ABSTRACT FROM AUTHOR]