Interchain order, soliton confinement, and electron-hole photogeneration in<i>trans</i>-polyacetylene

Two neighboring trans-polyacetylene chains are modeled individually by the Su, Schrieffer, and Heeger Hamiltonian and coupled by an interchain electron-transfer term. Geometrical considerations show that the interchain transfer integrals alternate in size and possibly even in sign. In the latter case parallel ordering of dimerization is favored. Due to the bonding produced by the splitting of midgap levels for parallel ordering, two neutral solitons on neighboring chains are strongly bound. The binding energy is calculated in the continuum limit using the analogy to the solvable model of a diatomic polymer chain. The direct inter$roman chain--- photoproduction of electron-hole pairs is calculated for the two orderings and for polarization perpendicular to the chain axis. It is found that not too far above threshold (\ensuremath{\omega}=2\ensuremath{\Delta}) this contribution is comparable to the intrachain optical absorption.

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