Electron localization in a percolating network: An ESR study of carbon-black/polymer composites

Abstract

The electronic susceptibility ${\mathrm{\ensuremath{\chi}}}_{\mathrm{e}}$ of conducting composites of carbon-black particles embedded in a nonconducting polymer matrix has been measured over a wide concentration and temperature range by electron-spin resonance (ESR). The onset of an extra Curie contribution to ${\mathrm{\ensuremath{\chi}}}_{\mathrm{e}}$ below ${10}^{2}$ K is seen as evidence for electron localization, as is the narrowing of the ESR line below 50 K. We show that Coulomb interactions have to be taken into account to explain these data and that the magnitude of the interaction is consistent with the value found previously from dc-conductivity data.