Polyacetylene Revisited

Abstract

The conjugated organic polymer (CH)_X has recently been the subject of extensive interest on two counts: 1) In pristine trans-(CH)_X, EPR and NMR evidence has been given for highly mobile spin carriers that carry no charge. These have been interpreted as arising from topological solitons (a localized reversal of the bond alternation pattern). The novelty of such spin carriers has stimulated much theoretical and experimental interest. 2) Upon doping, the conductivity of (CH)_X increases by ~10¹² and undergoes an apparent insulator-to-metal transition at ~1% dopant concentration. The possibility that the doping produces charged solitons rather than band electrons and that with increasing density this soliton gas undergoes a phase transtion has also attracted much interest.