CONDUCTION IN METALLIC TRANS-POLYACETYLENE

We consider conduction in heavily doped high conductivity polyacetylene samples for which the properties indicate a continuous density of states at the Fermi energy, at least in major portions of the sample. Data for conductivity as a function of temperature for many of these samples, as well as those of less conducting samples, have been well fitted by the three-parameter Sheng theory. This theory assumes that all of the current is due to tunneling between perfectly conducting metallic particles embedded in an insulator. We propose that, rather than being determined by tunneling, conductivity is limited primarily by conjugation defects and chain breaks within the metallic regions, the increase in conductivity with temperature being due to thermal activation over barriers arising from such defects. As background for discussing conduction, we review the properties of the metallic state, contrasting the predictions for the soliton lattice and polaron lattice. The question of whether the transverse conductivity is coherent or incoherent is considered, with the conclusion that neither theory nor experiment provides an answer to this question at present. Information about the transmission of known defects, such as sp3 and carbonyl defects, is summarized. Finally, examples are given for some types of barriers that can contribute to the observed increase of conductivity with temperature and a very general expression is given for resistivity variation with temperature of metallic samples. © 1990.