Weak localization, electron-electron interaction, and metal-insulator transition in ion-implanted polymers

Abstract

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 ∼ 10 2 S/cm after implantation. A metal-insulator transition is observed at T c ∼ 30 K. Above T c , the results of a negative magnetoresistance ( ΔR/ R( H, T)), a weakly temperature dependent conductivity ( σ( T) α T p , 0.5 < p < 1), a linearly T-dependent thermopower ( S( T)), a Pauli spin susceptibility ( χ Pauli ), and a large microwave dielectric constant ( ε 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 ΔR/ R, stronger T-dependent σ, and 1/ T-dependent S with a continued large and positive ε mw all suggest an increased e-e interaction effect which opens up a ‘Coulomb’ gap (∼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.