Electrodynamics of the conducting polymer polyaniline on the insulating side of the metal-insulator transition

Abstract

Conducting polymer samples of polyaniline (PANI) exhibit a dramatic change in their conductivity as a function of protonation level, analogous with the changes in the transport properties of semiconductors upon doping. In this paper, PANI samples were prepared by protonating with varying concentrations of hydrochloric acid. The complex terahertz frequency-dependent conductivity and the dc conductivity of these samples were measured and analyzed in the framework of the disorder-driven, metal-insulator quantum phase transition. The samples were determined to all fall in the insulating phase of this phase transition. The frequency dependence of both the real and imaginary terahertz conductivity are found to be consistent with theories that include electronic correlation effects.