Microwave complex impedance measurements on the heavy fermion superconductor UBe13

Abstract The complex microwave impedance in the frequency range of ≈ 8–36 GHz was measured in the superconducting state of a well-characterized heavy fermion single crystal of UBe 13 . This microwave photon energy ranges roughly from 15% to 60% of the zero-temperature (BCS) energy gap and is higher than previous measurements. Large changes are observed in the complex impedance when the sample is cooled below T c for all frequencies measured. The surface impedance cannot be described by the Mattis-Bardeen theory in the dirty limit for a conventional superconductor.