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 2mm × 2mm 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.