DOPING AND TEMPERATURE-DEPENDENCE OF ANISOTROPIC CONDUCTIVITY IN NEW POLYACETYLENE

We report on measurements of the conductivity of 'new' polyacetylene as a function of temperature for iodine and halide doping, for different dopant concentrations and for stretched and unstretched samples. The temperature dependence of conductivity in highly-doped stretched samples is remarkably similar parallel and perpendicular to the stretch direction, despite a difference in conductivity magnitudes by a factor of about 50. In particular, a maximum in the conductivity below room temperature (for AsF5 doping) is seen for the first time in the perpendicular as well as the parallel direction. The temperature dependence of the conductivity for the highly-doped stretched samples is in good agreement with a model of quasi-one-dimensional conduction combined with fluctuation-induced tunnelling through thin 'barriers' (for example chain defects). For unstretched samples, a model involving tunnelling between metallic islands gives a better description of the data.