Impurities in the heavy-fermion superconductor UBe13 (invited)

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Abstract
Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe13 to observe their effects on the superconducting and normal state properties. 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 that heavy Fermion superconductivity is only one of the possible ground states for heavy mass electron systems. All of the impurities tested resulted in a transition temperature depression.