NONLINEAR AC RESPONSE NEAR PERCOLATION-THRESHOLD AND 3-VARIABLE SCALING

We report on measurements of complex ac conductance of a random system of carbon-wax mixtures using both frequency (f) and amplitude (V) as measuring probes. The latter gives rise to nonlinear effects which necessitates modification of the usual two-variable scaling law. We propose a three-variable scaling form that reproduces our key experimental results summarized in the form of a R-f-V diagram (R is the inverse of the real part of the ac conductance). The results are also discussed in the context of some existing models.