Mesoscopic effects in macroscopic granular systems

Granular metals (systems of discontinuous metallic thin films) characterized by large distributions of grain sizes and inter-grain coupling were prepared by quench condensation. These samples, which are 2 mm x 2 mm in size, exhibit a number of experimental findings characteristic of low dimensional samples including magnetoresistance oscillations, sample-to-sample fluctuations and resistance switches. Such 'mesoscopic' effects are observed in a variety of metals such as Ni, Pb and Au. The results indicate that the transport in these systems is governed by a very small number of grains even though the sample contains about 109 grains. We interpret the findings as indications that the large distribution of resistances in the percolation network of the conduction trajectories facilitates the situation in which a small number of grains dominate the transport of the macroscopic system