We have found that at low temperatures the transport properties of carbon-poly(vinyl chloride) composites are governed by tunneling of carriers across a barrier that is modulated by temperature-activated fluctuations. The current-voltage characteristics can be divided into three regimes. At low dc fields the materials are Ohmic; at a critical dc field, the materials enter a thermally activated breakdown regime; above the breakdown field the $I-V$ characteristic may be studied with voltage pulses and the material is non-Ohmic. The dependence of the resistivity $\rho$ on temperature is discussed.

• Received 12 May 1978

DOI:https://doi.org/10.1103/PhysRevB.18.5712