Local superconducting coupling in the strong-localization limit of ultrathin granular metal films

The onset of fluctuations into the superconducting state, as identified by the appearance of a local minimum in the resistance versus temperature, is found to be coincident with the characteristic activation energy of normal-state conduction falling to a value of the order of the superconducting energy gap of the material at T=0. The model of conduction used is variable-range hopping with a Coulomb gap, appropriate to granular metals.