Low-Temperature Specific Heat and Pair-Breaking in Superconducting Zr6FeSb2

Abstract

The superconducting properties of Zr6FeSb2 were studied using low temperature specific heat measurements on polycrystalline samples prepared by arc-melting followed by annealing. The samples were nearly phase-pure Zr6FeSb2 with secondary phases constituting less than 2% as proved by the electron-probe microanalysis (EPMA). The specific heat exhibited a broad superconducting transition characterized by a peak at 0.75 K and a large residual electronic specific heat coefficient γres = 39 mJ/K2mol, which is approximately 57% of the normal-state coefficient γN. The large γres is unlikely to originate from the small amount of non-superconducting secondary phases. Instead, we attribute γres to significant pair-breaking effects caused by paramagnetic moments.