Microwave surface resistance of cuprate superconductors

Microwave surface resistance measurements have recently been playing an important role in assessing the suitability of superconducting materials for applications. The temperature (10-100K) dependence of the surface resistance of bulk polycrystalline ReBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (Re=Y, Gd and Sm) specimens at 27.4GHz has been extracted using a resonant cavity end wall replacement technique. The superconducting transition temperature was found to be increasing for rare earth atoms with larger ionic radius. The results seem to show that the surface resistance in the superconducting state is insensitive to the type of the rare earth ion and is mainly governed by the size of the superconducting grains and their alignment. The normal state surface resistance however is dependent on how well the grains are connected.