Optical absorption at photon energies less than the Peierls gap can occur via the direct production of a soliton-antisoliton pair. This involves a standard dipole electronic transition which is accompanied by a highly nonlinear lattice motion. We study the transition as a tunneling problem, using an extension of the instanton bounce methods of Coleman and Callan. We present the major results in simple physical terms. Comparison is made with recent measurements of the photoconductivity in polyacetylene.

• Received 3 May 1982

DOI:https://doi.org/10.1103/PhysRevB.26.3513