METAL NONMETAL TRANSITION IN POLYACETYLENE

We have studied a simple model of a nearly half-filled quasi-one-dimensional electron gas with both short-range electron-electron repulsion and retarded (phonon-mediated) attraction. We find that, as a function of doping (deviation from half-filling), there is the possibility of a transition from a (spinless) soliton state at low dopant concentration to a metallic state at higher concentration. Remarkably, we find that the metallic state is well approximated as a highly anisotropic non-interacting electron gas. These results are used to understand the metal-non-metal transition that has been observed in polyacetylene.