Finite Coherence Length of Thermal Noise in Percolating Systems
Abstract
Noise has been measured in two types of coductor-insulator mixtures as a function of bias and composition. It was marked by a huge increase in magnitude as the resistance increased only slightly due to Joule heating. The noise (resistance) current scale Is(Ir) for nonlinearity were found to scale with the linear resistance Ro as Is(Ir) Ro -xs(xr) where the exponent xs is equal to 0.80 and 0.68 in carbon-wax and carbon-polyethylene respectively and xr ≈ 0.5. It is shown that the large increase of noise in nonohmic regime as well as the differences between the noise and resistance exponents are due to the finite-sized inequilibrium thermal fluctuations whose coherence length is same as the correlation length of the underlying percolating systems. A expression for xs is derived.
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