Thermal-electrical breakdown of disordered conductor-insulator composites

We present the first observations of `thermal-electrical breakdown' in disordered conductor-insulator composites with a high electric field. This differs from simple electrical breakdown governed by local heat. When a large current flows through the most conductive pathway in a composite, the constriction of the current at the most electro-resistive point in the pathway increases the Joule heat dissipation, and a localized thermal-electrical domain `hot spot' appears on the composite. The thermal-electrical breakdown of the disordered conductor-insulator composite results from the local conductivity; the hot spot starts at the most resistive point on one of the most conductive pathways and the breakdown progresses as the hot spot evolves.