METAL-INSULATOR-TRANSITION IN HIGHLY CONDUCTING ORIENTED POLYMERS

We suggest that highly conducting oriented polymers with a fibril stru cture can be modeled by a regular lattice of disordered metallic wires with a random first-neighbor interwire coupling which mimics the cros s links between fibrils. We determine the position of the metal-insula tor transition (MIT) as a function of interwire cross-link concentrati on, interwire coupling J, and number M of polymer chains in a wire. Tw o different approaches are used. The first one is based on the self-co nsistent diagrammatic theory of Anderson localization. In the second a pproach, we show that the MIT can be described by a nonlinear sigma mo del. For M = 1, we find that a small value of J favors the metallic st ate while a large value of J induces localization in agreement with re cent numerical calculations. When M much greater than 1, an increase o f J always favors a delocalization of the electronic states in agreeme nt with a previous analytical analysis.