Electrical transport in granular metals

Abstract

In this paper, we studied the frequency-dependent AC conductance of randomly packed stainless steel spheres by means of impedance spectroscopy. Two types of power-law behaviour have been observed: (a) at low frequencies, the dependence of the measured impedance on the applied load; (b) at high frequencies, the dependence of the impedance modulus on frequency. Under different loading conditions, the imaginary parts of the measured conductances exhibit respective peaks at critical frequencies, corresponding to the onset of conductance dispersion. Using these critical points as scaling parameters to normalize the measured conductance, results in the spectra from different loading levels collapsing onto a single master curve. Both the electron tunnelling and capacitive paths among particles contribute to the conduction in granular metallic media, resulting in well-characterized universal behaviour.