We consider the continuum version of a one-dimensional model in which fermions are coupled with two phonon modes. Each mode is capable of producing dimerization, but together they are in competition, and the true ground state corresponds to only one of the two order parameters being nonzero in general. In the vicinity of a charged kink both order parameters are nonzero. We provide an analytical expression for the kink shape using the Fermi-level scheme which has been shown to be exact in another context. The gap-state energy and creation energy of the kink are also calculated. The model considered interpolates between the polyacetylene model and a model with continuous chiral symmetry in relativistic field theory.

• Received 21 September 1984

DOI:https://doi.org/10.1103/PhysRevB.31.3712