Microwave surface resistance measurements on the heavy fermion superconductor UPt3

The relative change of the microwave surface resistance has been measured a s a function of temperature in the superconducting and normal states of UPt 3 using a cavity perturbation technique. With our frequency range of simila r to 9-38 GHz, the microwave photon energy ((H) over bar omega) is similar to 20-95% of the estimated zero-temperature (BCS) energy gap (2 Delta(0)) o f UPt3. The surface resistance shows a change in slope as the signature of T-c and has a significantly weaker temperature dependence in the supercondu cting state than would be predicted by the Mattis-Bardeen theory. At higher frequencies, the slope tends to change by a smaller amount. No indication of collective modes at any of the frequencies was observed down to the lowe st temperatures measured (similar to 0.1 K). (C) 1999 Published by Elsevier Science B.V. All rights reserved.