LOW-TEMPERATURE THERMOELECTRIC-POWER OF THE METAL-HALIDE DOPED POLYACETYLENE

We have measured thermoelectric power (TEP) of the doped polyacetylene (PA) from room temperature down to liquid helium temperature. The dop ants are AuCl3, NbCl5, FeCl3 and I-2. The overall TEP data show the di ffusive metallic property, i.e. the TEP is positive and it decreases q uasi-linearly upon cooling. For the metal-halide doped PA, the TEP is temperature independent with small magnitude about 0.2 similar to 0.6 mu V/K below 17K, while the quasi-linear temperature dependent TEP is observed for the iodine doped PA in the same low temperature regime. T he concentration dependence of TEP for AuCl3 doped PA shows that the T EP becomes negative at T<20K similar to 30K depending on the doping co ncentration with a broad minimum peak at low temperature. The result i ndicates that the effect of dopant to the PA chain is important to und erstand the metallic nature of heavily doped PA.