Electrical conductance of a 2D packing of metallic beads under thermal perturbation

Electrical conductivity measurements on a 2D packing of metallic beads have been performed to study internal rearrangements in weakly perturbed granular materials. Small thermal perturbations lead to large non-Gaussian conductance fluctuations. These fluctuations are found to be intermittent in time, with peaks gathered in bursts. The distribution of the waiting time Δ t between two peaks is found to be a power law Δ t −(1 + α t ) inside bursts. The exponent α t is independent of the bead network, the intensity of perturbation and external stress. These bursts are interpreted as the signature of individual bead creep rather than collective vault reorganisations. We propose a simple model giving α t = 1 − ζ, where ζ is the roughness exponent of the surface of the beads.