Heterogeneous model for conduction in conducting polymers and carbon nanotubes

The electronic transport properties of organic conducting polymers show remarkably similar behaviour patterns, and some aspects of this behaviour are also seen in mats of single-wall carbon nanotubes and bundles of (SN)x polymer fibres. Data for these materials provide further evidence for a series heterogeneous model for conduction, which can explain the crossover in the sign of the temperature dependence of the conductivity from nonmetallic to metallic; the model can also account for the metallic behaviour of thermoelectric power and the peak in the optical conductivity as a function of frequency observed in the polymers. The linear thermopower in highly-conducting polyacetylene and polyaniline indicates that there is no overall change in the nature of the electronic states near the crossover in conductivity temperature dependence, and also suggests an absence of significant superconductivity arising from the electron-phonon mechanism.