Influence of impurities and magnetic fields on the normal and superconducting states of UBe13.

Small amounts of Th and Lu impurities considerably affect both the low-temperature normal and the superconducting states of UBe13. Th enhances the electronic specific-heat parameter for T0 K and leads to a second phase transition in the superconducting state. Lu substitution for U suppresses superconductivity quite effectively, and also is sizably reduced. Bulk measurements confirm the unusual Hc2(T) curve of UBe13 that was previously obtained from electrical resistivity experiments. © 1986 The American Physical Society