Evidence for two superconducting gaps in the unconventional superconductor PrPt4Ge12

Abstract

We report the results of magnetization measurements on the unconventional superconductor PrPt4Ge12 in its superconducting state. A distinct positive curvature is observed in the temperature dependence of the lower critical field H C1(T) and the upper critical field H C2(T) around 5.5 K. The zero field critical current density J C(T, H = 0) is found to vary nearly linearly with temperature. We argue that these observed features are due to the existence of two superconducting gaps in the material. The normalized superfluid density is estimated from the temperature dependence of H C1. Our detailed analysis of the normalized superfluid density using a two-gap model indicates the presence of line nodes in the larger gap. The H C2(T) line can be fitted with the Usadel equations, and the positive curvature in H C2(T) is shown to be consistent with the two-gap picture of superconductivity.