Some aspects of electrical conduction in

granular systems of various dimensions

M. Creyssels1, S. Dorbolo2, A. Merlen1, C. Laroche1, B. Castaing1 and  E. Falcon1,*

  1 Laboratoire de Physique, Ecole Normale Supérieure de Lyon, CNRS UMR 5672, 69 007 Lyon, France
2 GRASP Photopôle, Physics Department, Université de Liège, B-4000 Liège, Belgium
* Present address: MSC, Université Paris Diderot - Paris 7, CNRS UMR 7057, 75 013 Paris, France


European Physical Journal E 23, 255 - 264 (2007)

DOI: 10.1140/epje/i2006-10186-9


We report on measurements of the electrical conductivity in both a 2D triangular lattice of metallic beads and in a chain of beads. The voltage/current characteristics are qualitatively similar in both experiments. At low applied current, the voltage is found to increase logarithmically in a good agreement with a model of widely distributed resistances in series. At high enough current, the voltage saturates due to the local welding of microcontacts between beads. The frequency dependence of the saturation voltage gives an estimate of the size of these welded microcontacts. The DC value of the saturation voltage ( ~ 0.4 V per contact) gives an indirect measure of the number of welded contact carrying the current within the 2D lattice. Also, a new measurement technique provides a map of the current paths within the 2D lattice of beads. For an isotropic compression of the 2D granular medium, the current paths are localized in few discrete linear paths. This quasi-onedimensional nature of the electrical conductivity thus explains the similarity between the characteristics in the 1D and 2D systems. 

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