Microwave measurements on the heavy fermion superconductors UPt3 and UBe13

The complex microwave impedance at ∼11.5 GHz was measured in the superconducting state of two well characterized heavy fermion single crystals, UPt 3 and UBe 13 . This microwave photon energy is about 30% and 20% of the zero-temperature energy gap, respectively, and is higher than previous measurements. The results for UBe 13 seem to be well described by the Mattis-Bardeen theory in the dirty-limit for a conventional superconductor. However, the behavior in UPt 3 deviates from this conventional theory even when paramagnetic impurity scattering effects are taken into account.