Evidence for multiple superconducting gaps in the filled skutterudite compound LaRu4As12

Superconducting properties of the filled skutterudite compound LaRu4As12 were investigated both as a function of temperature andmagnetic field. At T << T-c = 10.45 K, the electronic contribution to the specific heat was found to be at variance with the predictions for an s-wave superconductor with one energy gap. In constant applied fields up to H-c2(0) approximate to 10.2 T, multiple gaps have been further inferred from both a nonlinear magnetic-field dependence of the specific heat in the zero-temperature limit and a positive curvature of the upper critical field in the vicinity of T-c. Thus, LaRu4As12 appears to be a rare multiple-gap superconductor with cubic symmetry. Intriguing evidence for multiband effects is observed in the compound with enhanced superconducting properties as compared to other skutterudite superconductors.