Non-Gaussian conductance noise in disordered electronic systems due to a nonlinear mechanism

We present the results of conductance-noise experiments on disordered films of crystalline indium oxide with lateral dimensions 2 μm-1 mm. The power spectrum of the noise has the usual 1 f form, and its magnitude increases with the inverse sample volume down to the sample size of 2 μm, a behavior consistent with uncorrelated fluctuators. A colored second spectrum is only occasionally encountered (in samples smaller than 40 μm), and the lack of systematic dependence of non-Gaussianity on sample parameters persisted down to the smallest samples studied (2 μm). Moreover, it turns out that the degree of non-Gaussianity exhibits a nontrivial dependence on the bias V used in the measurements; it initially increases with V then, when the bias is deeper into the nonlinear transport regime it decreases with V. We describe a model that reproduces the main observed features and argue that such a behavior arises from a nonlinear effect inherent to electronic transport in a hopping system and should be observed whether or not the system is glassy.