The superconductor insulator transition in systems of ultrasmall grains

We present transport measurements on quench condensed granular Pb films in which the grains are about 40-80 Angstrom in diameter. These films show a crossover from an insulator to a superconductor behavior as the nominal thickness of the layer is increased. This transition is different in nature than those seen in quench condensed systems reported in the past where the films were either uniform or granular with grain diameters on the order of 200 Angstrom. We discuss possible physical mechanisms for these transitions. (C) 2003 Elsevier B.V. All rights reserved.