Nonlinear transport and 1/f noise in insulators

We introduce and analyze a class of nonlinear Langevin equations that describe electrical transport in systems with electric-field thresholds, such as charge-density-wave systems biased just above threshold. For sufficiently large nonlinearities, the models are argued to exhibit scale-invaraint phases wherein spatial and temporal correlations decay algebraically; in particular, current and voltage fluctuations show 1/f noise with universal exponents. The values of physical parameters required for the experimental observation of these phases are estimated. © 1992 The American Physical Society.