Disorder-induced metal-insulator transition in conducting polymers

The metal-insulator (M-I) transition in conducting polymers is particularly interesting: critical behavior has been observed over a relatively wide te mperature range in a number of systems, including polyacetylene, polypyrrol e, poly (p-phenylene vinylene), and polyaniline. In each case, metallic, cr itical, and insulating regimes have been identified through Zabrodskii plot s of the logarithmic derivative of the conductivity. The critical regime (i n which the conductivity varies as T-beta, where beta approximate to 1/3) i s tunable by varying the extent of disorder and by applying external pressu re and/or an external magnetic field. The transitions from metallic to crit ical behavior and from critical to insulating behavior have been induced wi th a magnetic field and from insulating to metallic behavior with applied p ressure.