Metal-insulator transition in PF6 doped polypyrrole: interchain charge transfer versus electronic correlation

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We performed dielectric spectroscopy on polypyrrole near the metal-insulator transition (MIT) down to 2 K. We evaluate the dependence of the plasma frequency and the scattering time (t) on the distance to the MIT, characterized by the Fermi-level relative to the band-edge of extended states, EF-Ec. Especially the strong decrease of t with increasing EF-Ec is in conflict with the usually applied models for the MIT. Although morphology and disorder are important, the MIT is Mott-Hubbard-like being dominated by the competition of interchain charge transfer and electronic correlation.