The critical regime of the metal-insulator transition in conducting polymers: Experimental studies

The metal-insulator (M-I) transition in conducting polymers is particularly interesting: critical behavior has been observed over a relatively wide temperature range in a number of systems, including polyacetylene. polypyrrole. poly (phenylene vinylene) and polyaniline. In each case. metallic, critical and insulating regimes have been identified through Zabrodskii plots of the logarithmic derivative of the conductivity. The critical regime (in which the conductivity varies as T-beta, where beta approximate to 1/3) is tunable by varying the extent of disorder and by applying external pressure and/or an external magnetic field. The transitions from metallic to critical behavior and from critical to insulating behavior have been induced with a magnetic field and from insulating to metallic behavior with applied pressure.