Impurity effects in UBe13

The effect of a few per cent of thorium replacing uranium in the heavy-fermion superconductor UBe13 is dramatic. The low-temperature properties are drastically altered and a second transition of a controversial nature occurs below the onset of superconductivity. Other non-magnetic impurities are seen from various preliminary measurements to yield promise of different results. Normally such impurity studies show only gradual changes in properties, which are useful for extracting superconducting parameters, but the large effects seen in this heavy-fermoin superconductor highlight its exotic nature. © 1985