Percolative behavior of the superconductive transition ofYBa2Cu3O7films

The superconductive transition of c-axis-oriented YBa2Cu3O7 thin films, as characterized by measurements of the temperature dependence of the magnetic penetration depth, is found to occur below the Ginzburg-Landau mean-field transition. The divergence of the penetration depth at the transition is in good quantitative agreement with the predictions of a percolation model.