Carrier transport in polyacetylene with intermediate doping.

Abstract

By use of a modified version of Naarmann's method, we have synthesized polyacetylene (CH${)}_{\mathit{x}}$. The doping was carried out in liquid phases of iodine and iron chloride, and the samples obtained were [CH(${\mathrm{I}}_{3}$${)}_{\mathit{y}}$${]}_{\mathit{x}}$ and [CH(${\mathrm{FeCl}}_{4}$${)}_{\mathit{y}}$${]}_{\mathit{x}}$, respectively. The dopant concentration y is between 0.01 and 0.05, and belongs to the intermediate doping region. The temperature dependence of the dc conductivity for the different dopant concentrations is measured. In doped trans-polyacetylene, charged and neutral soliton pairs are produced in the chains. The conduction mechanism, which is based on the intersoliton hopping of electrons, is the same for polyacetylene with intermediate or light doping. For this reason, Kivelson's model of the average hopping rate, the Hamiltonian of trans-polyacetylene explored by Su, Schrieffer, and Heeger, and the method of Ambegaokar, Halperin, and Langer, which is related to the average transition rate, are used and the relation between the average hopping rate and the transition rate obtained. Finally, in the light of percolation theory and the variable-range-hopping model, the formula for conductivity is derived. The theory is in good agreement with the experiments.