MICROWAVE CONDUCTIVITY OF PATTERNED YBA2CU3O7 THIN-FILMS

We have used coplanar resonators to provide a sensitive measure of the ab-plane microwave complex conductivity sigma = sigma(1)f - i sigma(2 ) at 8 and 16 GHz of high quality, patterned thin films of YBa2Cu3O7-d elta on MgO substrates, No BCS coherence effects were observed in sigm a(1)(T) below T-c. Instead, we observe a broad peak centred between 40 and 50 K, which was present in all of the samples, The T dependence o f the magnetic penetration depth lambda(T) = (omega mu(0) sigma(2)(T)) (-1/2) also differed from that expected for a BCS superconductor in th e London limit, This difference is most noticeable at low T, where ins tead of the usual exponential T dependence, we observe a term in T-2 f or every sample, We discuss briefly the effects of sample oxygenation bn these results.