THE ROLE OF MICROGEOMETRY IN THE ELECTRICAL BREAKDOWN OF METAL-INSULATOR MIXTURES

The breakdown phenomena of percolative metal-insulator composites and their extreme sensitivity to fine details of the microgeometry are dis cussed, for three different cases: the critical current of superconduc tor-insulator mixtures (or superconductor-normal metal); the dielectri c breakdown of metal-insulator composites below the percolation thresh old (insulating regime); and the electrical breakdown above the metal- insulator transition (metallic regime). Two experimental techniques fo r characterizing the microgeometry are described: (a) 1/f noise measur ements, which provide the fourth moment of the current distribution; ( b) the harmonic generation method, where the weakly nonlinear electric al response due to local Joule heating provides information on the fou rth (and higher) moment of the current distribution.