WEAK-LOCALIZATION, ELECTRON-ELECTRON INTERACTION, AND METAL-INSULATOR-TRANSITION IN ION-IMPLANTED POLYMERS

Kr+ ion implanted rigid rod PBO, PBT and ladder BBL polymers show similar transport and optical behavior, with room temperature conductivities increasing from 10(-12) S/cm to approximately 10(2) S/cm after implantation. A metal-insulator transition is observed at T(c) approximately 30 K. Above T(c), the results of a negative magnetoresistance (DELTAR/R(H, T)), a weakly temperature dependent conductivity (sigma(T) is-proportional-to T(p), 0.5 < p < 1), a linearly T-dependent thermopower (S(T)), a Pauli spin susceptibility (chi(Pauli)), and a large microwave dielectric constant (epsilon(mw)) resemble those of disordered metals in which weak localization and e-e interactions dominate the charge transport. Below T(c), the changed behavior of positive DELTAR/R, stronger T-dependent sigma, and 1/T-dependent S with a continued large and positive epsilon(mw) all suggest an increased e-e interaction effect which opens up a 'Coulomb' gap (approximately 2meV), likely due to the enhanced localization. The density of states (DOS) is zero only at the center of the gap in accord with the theoretical prediction of the 'Coulomb' gap.