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 dopants are AuCl3, NbCl5, FeCl3 and I2. The overall TEP data show the diffusive metallic property, i.e. the TEP is positive and it decreases quasi-linearly upon cooling. For the metal-halide doped PA, the TEP is temperature independent with small magnitude about 0.2~0.6μV/K below 17K, while the quasi-linear temperature dependent TEP is observed for the iodine doped PA in the same low temperature regime. The concentration dependence of TEP for AuCl3 doped PA shows that the TEP becomes negative at T<20K~30K depending on the doping concentration with a broad minimum peak at low temperature. The result indicates that the effect of dopant to the PA chain is important to understand the metallic nature of heavily doped PA.