Impurities in the heavy-Fermion superconductor UBe13

Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe13 to observe their effects. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest tat heavy Fermion behavior is only a necessary condition for heavy Fermion superconductivity. All of the impurities tested resulted in a transition temperature depression