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

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