Spin and charge excitations in polyacetylene

Abstract

Abstract Spin and charge excitations in pristine and AsF5-doped polyacetylene have been investigated to resolve the issue of whether or not topological solitons have been observed. We present experimental results for both materials suggesting that the simple model from which the soliton-based interpretations have been derived is inapplicable. In pristine trans-polyacetylene, both protonated and deuterated, conclusions are deduced from spin-echo and continuous-wave EPR about the spin diffusion rate, its temperature dependence and anisotropy that contradict predictions of the soliton theory. In AsF5-doped cis-polyacetyelene, we conclude from magnetic and transport measurements that the doping is very inhomogeneous, the doped and undoped parts being largely distinct with the doped regions metallic. The conductivity changes previously interpreted as arising from a transition wthin the doped region are attributed to a change in the topology of these regions, i. e. the crossing of a percolation threshold to a r...