TEMPERATURE-DEPENDENCE OF THE PENETRATION DEPTH OF YBA2CU3O7-DELTA FILMS NEAR T-C

The temperature dependence of the penetration depth, lambda, of films of YBa2Cu3O7-delta measured using radio frequency techniques, has been found to have a mean-field-like exponent well within some estimates o f the critical region. This result is found only if finite-size bounda ry conditions at the film edge are included in the analysis. This obse rvation agrees with a recent renormalization group calculation in whic h the critical exponent for lambda is mean-field-like, while the other s are XY-like. It could also imply that the critical regime has not be en reached, but then recent heat capacity measurements with XY-like be havior would have to be flawed.