Low-energy conductivity ofPF6-doped polypyrrole

In this paper we present a set of temperature-dependent reflectivity and dc conductivity measurements on a series of ${\mathrm{PF}}_6$-doped polypyrrole samples differing only in their synthesis temperatures, spanning the metal-insulator transition. From the reflectivity we have derived optical constants, taking particular care that they are Kramers-Kronig consistent. We have analyzed our data in the light of two proposed models for the structure of conducting polymers, homogeneous and inhomogeneous disorder, and find that the observed decrease in the low-energy ac conductivity can be accounted for by a simple generalization of the heterogeneous disorder model used to explain the dc conductivity. The homogeneous localization-modified Drude model fails to satisfactorily model the ac conductivity at low energy.