Electron hopping in a soliton band: Conduction in lightly doped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mn/><mml:mo>(</mml:mo><mml:mi mathvariant="normal">CH</mml:mi><mml:mo>)</mml:mo><mml:mn/></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>

On the basis of both theoretical and experimental studies, it has been suggested that the low-energy charge-excitations introduced into polyacetylene by light doping are charged solitons. However, these solitons are normally bound to oppositely charged impurities so that soliton conduction is inefficient at room temperature and below. In the presence of both charged and neutral solitons an alternative conduction mechanism is possible; phonon-assisted hopping between the localized electronic midgap states associated with the soliton. This is a novel process as it involves hopping between dynamical defects. The theory of this process is developed in detail in terms of a three-dimensional generalization of the microscopic model of Su, Schrieffer, and Heeger, and found to be consistent with experiment. Because of the disorder, namely the random distribution of impurities, the conduction pathways are essentially three dimensional, with interchain hops dominating intrachain hops.

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