Quantum hopping in metallic polymers

Highly conducting polymers such as polyaniline and polypyrrole in a metallic state have unusual frequency-dependent conductivity, including multiple zero crossing of the dielectric function. A low-frequency electromagnetic response in terms of a Drude metal is provided by an extremely small fraction of the total number of conduction electrons similar to0.1% but with extremely high mobility or anomalously long scattering time similar to10(-13) s. We show that a network of metallic grains connected by resonance quantum tunneling has a Drude-type response for both the high- and low-frequency regimes and behaves as a dielectric at intermediate frequency in agreement with experimental observations. The metallic grains in polymers represent crystalline domains of well-packed chains with delocalized electrons embedded in the amorphous media of poor chain order. Intergrain resonance tunneling occurs through the strongly localized states in the amorphous media. (C) 2003 Elsevier B.V. All rights reserved.