We have experimentally studied a model system that demonstrates the crossover from a superconductor that is dominated by phase fluctuations, to one in which the amplitude of the order parameter is the controlling influence on T c. This model system is comprised of two-dimensional granular Pb with an overlayer of Ag. The system displays many aspects of the phase diagram of the concentration dependence of T c in the high-T c superconductors, and this crossover has been applied to explain the phase diagram in that case. We point out the similarities and differences between the model system presented in this paper and the high-T c superconductors.

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We report on a study of proximity effects in quench‐condensed superconducting (Pb) and ferromagnetic (Ni) granular films in which we are able to deposit sequential layers of material and measure transport and magnetoresistance properties in‐situ for different degrees of material coverage. We find that adding a normal (non‐superconducting or non‐ferromagnetic) overlayer to isolated Pb or Ni grains enhances long‐range order in the film. We interpret these results as being due to proximity effects where the grains are coupled via the weak order‐parameter induced in the overlayer material.