Magnetoresistance of the metallic polyacetylene

The temperature dependence of the zero field resistivity, ρ(T), and the magnetoresistance (MR) of polyacetylene (PA) doped with iodine, metal-halide (AuCl₃, FeCl₃) and perchlorate are measured. The results of doped PA are different for each dopant and for the degree of aging. The ρ(T) of the metal-halide and the perchlorate doped PAs show a resistivity minimum near T^* ≈ 200 K and the weak temperature dependence at low temperature. In particular, some of the perchlorate doped PA samples show the positive temperature coefficient of resistivity (TCR) from T = 1.5 K to T = 300 K with resistivity ratio ρ(T = 1.5 K)/ρ(T = 300 K) = 0.5 approx. 0.7 depending on the samples. The MR is negative for all of the metallic PA samples. Both transverse (J ⊥ H) and longitudinal (J∥H) MR show similar magnetic field dependencies, although the magnitude of the transverse MR is larger than that of the longitudinal MR. For the aged samples, the ρ(T) increase more rapidly upon cooling than that of the fresh samples. The MR of the aged samples is positive. The localization-interaction theory is examined for the observed ρ(T) and MR data of doped PA. But the model of interchain charge transfer bridged by the dopants seems to explain the negative MR as well as the metallic temperature dependence of resistivity for the perchlorate doped polyacetylene.