Weakly Nonlinear Conductivity and Flicker Noise Near Percolation

This short review describes developments over the last decade in the study of a special type of transport, namely, weakly nonlinear conductivity and the closely related conductance fluctuation noise, in percolation systems. These phenomena are much more sensitive than linear transport properties to the special microgeome-try of the infinite percolation cluster. As a result they exhibit a much richer critical behavior in the vicinity of a percolation threshold. In particular, the noise always as-sumes a maximum at the threshold and the weakly nonlinear conductivity may exhibit either monotonic or non-monotonic critical behavior, depending on the properties of the components. In the case of non-monotonic behavior, the nonlinear conductivity at the threshold may be larger than that of both components, which leads to an enhancement of nonlinear effects in such systems. Either the good conductor or the poor conductor may dominate the critical behavior both above and below the threshold. These prop-erties were studied by numerical simulations on random resistor networks, an effective medium type approximation and a scaling theory.