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 simi lar transport and optical behavior, with room temperature conductiviti es increasing from 10(-12) S/cm to approximately 10(2) S/cm after impl antation. A metal-insulator transition is observed at T(c) approximate ly 30 K. Above T(c), the results of a negative magnetoresistance (DELT AR/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 microwa ve dielectric constant (epsilon(mw)) resemble those of disordered meta ls in which weak localization and e-e interactions dominate the charge transport. Below T(c), the changed behavior of positive DELTAR/R, str onger T-dependent sigma, and 1/T-dependent S with a continued large an d positive epsilon(mw) all suggest an increased e-e interaction effect which opens up a 'Coulomb' gap (approximately 2meV), likely due to th e enhanced localization. The density of states (DOS) is zero only at t he center of the gap in accord with the theoretical prediction of the 'Coulomb' gap.