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

Abstract : 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 distributions of the waiting time ∆t between two peaks is found to be a power-law ∆t −(1+αt) inside bursts. The exponent αt 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 αt = 1 − ζ, where ζ is the roughness exponent of the surface of the beads