Mesoscopic effects in macroscopic granular systems

Abstract

Granular metals (systems of discontinuous metallic thin films) characterized by large distributions ofgrain sizes and inter-grain coupling were prepared by quench condensation. These samples, which are2 mm × 2 mm in size, exhibit a number of experimental findings characteristic of low dimensionalsamples including magnetoresistance oscillations, sample-to-sample fluctuations andresistance switches. Such ‘mesoscopic’ effects are observed in a variety of metals suchas Ni, Pb and Au. The results indicate that the transport in these systems isgoverned by a very small number of grains even though the sample contains about109 grains. We interpret the findings as indications that the large distribution of resistances inthe percolation network of the conduction trajectories facilitates the situationin which a small number of grains dominate the transport of the macroscopicsystem.