EVIDENCE FOR A NON-S-WAVE SUPERCONDUCTING ORDER-PARAMETER IN YBA2CU3O6.6 WITH T-C=60 K

Several recent phase-sensitive-tunneling experiments have indicated th at YBa2Cu3O6.9 is not an s-wave superconductor. In this work we report an analogous experiment on a related cuprate superconductor, YBa2Cu3O 6.6, with T-c=60 K. The critical current vs applied field of a Pb-YBa2 Cu3O6.6 single crystal corner Josephson junction is measured and compa red with the theory. As a control experiment, measurements are made on a Pb-YBa2Cu3O6.6 edge junction. The results are consistent with a d-w ave order parameter for YBa2Cu3O6.6. It is thus unlikely that the resu lts of previous similar experiments on almost fully oxygenated YBa2Cu3 O6.6 may simply be explained by the presence of the Cu-O chains.