Interchain coupling in polyacetylene

Abstract

The interchain coupling between two polyacetylene chains is considered, both in the absence of solitons, and with one neutral soliton on each chain. A new correction to the size and position of the band gap is found in the former case, and when solitons are present it is shown that their mid-gap levels interact. In this case the differences between the matched (same dimerization pattern at ± ∞) and the mismatched cases (opposite pattern at ± ∞) are clearly illustrated. The mid-gap level splitting is found to be ΔE = t⟩ l/ξ sinh l/ξ, in the matched case, and ∼ 0(e-kfξ) in the mismatched case (where l is the soliton separation, kf the Fermi wavevector, ξ the soliton width, and [1] kf ξ ∼ 10). This interaction increases the strength of the 3 D pinning of solitons, there-fore strengthening the case against the solitonic model for conduction in polyacetylene. It also predicts the existence of a critical density ρc ∼ 0.05 of solitons, at which the preferred local ordering between chains switches from mismatched to matched dimerization