Nature of insulator–metal transition and novel mechanism of charge transport in the metallic state of highly doped electronic polymers

• Published in: Synthetic metals Vol. 125; no. 1; pp. 43 - 53
• Main Authors: Prigodin, V.N., Epstein, A.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 02-11-2001
• Subjects: Conducting polymers; Dielectric spectroscopy; Network model; Resonant quantum tunneling; Transport properties; Conducting polymers; Dielectric spectroscopy; Transport properties; Network model; Resonant quantum tunneling
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/S0379-6779(01)00510-0

Highly conducting polymers such as polyaniline and polypyrrole in a metallic state have unusual frequency dependent conductivity, including multiple zero crossings of the dielectric function. A low frequency electromagnetic response, when be analyzed by the Drude theory of metals, is provided by an extremely small fraction of the total number electrons ∼0.1%, but with extremely high mobility or anomalously long scattering time ∼10
−12
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 amorphous media. The small concentration of electrons participating in dc-transport is assigned to the low density of resonance states, and the long relaxation time is related to the narrow width of energy levels in resonance.