SOLITON MODEL OF METALLIC STATE IN POLYACETYLENE

Doping of polyacetylene by more than 4-7% causes an insulator-metal tr ansition, as evidenced by the appearance of sizable Pauli susceptibili ty and large conductivity. The nature of the metallic state has been t he subject of wide speculation. We show that there is strong evidence, mainly from optical absorption measurements, that the soliton lattice characteristic of doped polyacetylene below the transition persists i n the metallic state. Another strong piece of evidence for the soliton lattice model is the existence of samples in which free carrier absor ption is present at 300 K, but disappears at low temperatures. We show that other proposed models of the metallic state (polaron lattice, un iform chain and polson model) cannot explain the data.