Fluctuation-induced tunneling conduction in disordered materials Ping Sheng RCA Laboratories, Princeton, New Jersey 08540 (Received 30 April 1979) In disordered materials with large conducting regions separated by small insulating barriers, electrical conduction is attributed to a novel mechanism: fluctuation-induced tunneling. This mechanism involves thermally activated voltage fluctuations across insulating gaps, which influence the temperature and field dependences of conductivity. Theoretical expressions for tunneling conductivity are derived, showing thermally activated behavior at high temperatures and temperature-independent behavior at low temperatures. The temperature dependence of conductivity is controlled by the shape of the tunneling barrier. A high-field tunneling current expression is also obtained, showing that tunneling current increases nonlinearly with field, but the nonlinearity decreases with temperature, indicating effective lowering and narrowing of the barrier by voltage fluctuations. The theory is generalized to a random network of tunnel junctions using the effective-medium theory. Theoretical predictions are compared with experimental results for three disordered systems: carbon-polyvinylchloride composites, heavily doped GaAs, and doped polyacetylene. In each case, excellent agreement is found. The nonmetallic temperature dependence of resistivity in doped polyacetylene samples is explained by the theory. The paper discusses voltage fluctuations in disordered materials, showing that they play a significant role in modifying electron tunneling probability. Theoretical calculations of fluctuation-induced tunneling characteristics for a single junction and generalization to a random network are presented. The theory is applied to three disordered systems, showing excellent agreement with experimental results. The paper also discusses the parabolic barrier approximation and its application to the theory. The effective-medium theory is used to generalize the theory to a random network of tunnel junctions. The paper concludes that fluctuation-induced tunneling is a valid mechanism for conduction in disordered materials, with the theory successfully explaining experimental results.Fluctuation-induced tunneling conduction in disordered materials Ping Sheng RCA Laboratories, Princeton, New Jersey 08540 (Received 30 April 1979) In disordered materials with large conducting regions separated by small insulating barriers, electrical conduction is attributed to a novel mechanism: fluctuation-induced tunneling. This mechanism involves thermally activated voltage fluctuations across insulating gaps, which influence the temperature and field dependences of conductivity. Theoretical expressions for tunneling conductivity are derived, showing thermally activated behavior at high temperatures and temperature-independent behavior at low temperatures. The temperature dependence of conductivity is controlled by the shape of the tunneling barrier. A high-field tunneling current expression is also obtained, showing that tunneling current increases nonlinearly with field, but the nonlinearity decreases with temperature, indicating effective lowering and narrowing of the barrier by voltage fluctuations. The theory is generalized to a random network of tunnel junctions using the effective-medium theory. Theoretical predictions are compared with experimental results for three disordered systems: carbon-polyvinylchloride composites, heavily doped GaAs, and doped polyacetylene. In each case, excellent agreement is found. The nonmetallic temperature dependence of resistivity in doped polyacetylene samples is explained by the theory. The paper discusses voltage fluctuations in disordered materials, showing that they play a significant role in modifying electron tunneling probability. Theoretical calculations of fluctuation-induced tunneling characteristics for a single junction and generalization to a random network are presented. The theory is applied to three disordered systems, showing excellent agreement with experimental results. The paper also discusses the parabolic barrier approximation and its application to the theory. The effective-medium theory is used to generalize the theory to a random network of tunnel junctions. The paper concludes that fluctuation-induced tunneling is a valid mechanism for conduction in disordered materials, with the theory successfully explaining experimental results.