Disorder-induced neutral solitons in degenerate ground state polymers

We study the effects of weak off-diagonal disorder on pi-conjugated polymer s with a doubly degenerate ground-state. We find that disorder induces a fi nite density of neutral solitons in the lattice dimerization of a polymer c hain. Interchain interactions result in a linear potential between the soli tons and, if sufficiently strong, bind them into pairs resulting in an expo nential suppression of the soliton density. As neutral solitons carry spin 1/2, they contribute to the polymer's magnetic properties. We calculate the magnetic susceptibility and suggest measurements of the magnetic susceptib ility in trans-polyacetylene at low temperatures.