MEASUREMENTS OF THE TEMPERATURE-DEPENDENCE OF THE MAGNETIC PENETRATION DEPTH IN YBA2CU3O7-DELTA SUPERCONDUCTING THIN-FILMS

Using a very sensitive microstrip-resonator technique, we have measured lambda(T) of c-axis YBa2Cu3O7-delta films on various substrates and compared the results to similar data on Nb and NbCN films. For YBa2Cu3O7-delta, lambda (T) is found to be exponential and not power law in its temperature dependence (for T < T(c)/2) in the best films. Overall the data cannot be described by a single-gap BCS temperature dependence. The data at low temperature provide a lower limit of 2-DELTA(0)/k(B)T(c) almost-equal-to 2.5 for the minimum gap in YBa2CuO7-delta, yet show strong-coupling-like behavior at high temperatures. We discuss our results in the context of other experiments on the cuprate superconductors.