Europhys. Lett.
Volume 65, Number 2, January 2004
Page(s) 186 - 192
Section Electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics
Published online 01 January 2004
Europhys. Lett., 65 (2) , pp. 186-192 (2004)
DOI: 10.1209/epl/i2003-10071-9

"Turbulent" electrical transport in copper powders

E. Falcon, B. Castaing and C. Laroche

Laboratoire de Physique, École Normale Supérieure de Lyon UMR 5672 - 46, allée d'Italie, 69007 Lyon, France

(Received 28 February 2003; accepted in final form 6 November 2003)

Compressed copper powder has a very large electrical resistance (1 $\un{M \Omega}$), due to the oxide layer on grains (100 $\un{\mu
m}$ ). We observe that its voltage-current U- I characteristics are nonlinear, and undergo an instability, from an insulating to a conductive state at relatively small applied voltages. Current through the powder is then noisy, and the noise has interesting self-similar properties, including intermittency and scale invariance. We show that heat dissipation plays an essential role in the physics of the system. One piece of evidence is that the instability threshold always corresponds to the same Joule dissipated power whatever the applied stress. In addition, we observe long-time correlations which suggest that thermal expansion locally creates or destroys contacts, and is the driving mechanism behind the instability and noise observed in this granular system.

45.70.-n - Granular systems.
05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.
72.80.-r - Conductivity of specific materials.

© EDP Sciences 2004