Soliton diffusion in polyacetylene. III. Low-temperature regime

The soliton diffusion in the temperature region $T<\mathrm{}{T}_0\left(\equiv 2m{c}^2\right)$ is analyzed theoretically within the Su, Schrieffer, and Heeger model. Here $m$ is the soliton mass and $c$ is the acoustic-phonon velocity. It is shown that the diffusion constant increases exponentially like $\exp \left(\frac{T_0}{T}\right)$ as the temperature $T$ is decreased below $T_0$. This temperature dependence appears to be consistent with some of the recent nuclear-magnetic-resonance experiments in pristine polyacetylene.