Magnetoresistance of the metallic polyacetylene

The temperature dependence of the zero field resistivity, rho(T), and the m agnetoresistance (MR) of polyacetylene (PA) doped with iodine, metal-halide (AuCl3, FeCl3) and perchlorate are measured. The results of doped PA are d ifferent for each dopant and for the degree of aging. The rho(T) of the met al-halide and the perchlorate doped PAs show a resistivity minimum near T* approximate to 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 w ith resistivity ratio rho(T = 1.5 K)/rho(T = 300 K) = 0.5 similar to 0.7 de pending on the samples. The MR is negative for all of the metallic PA sampl es. Both transverse (J perpendicular to H) and longitudinal (J parallel to H) MR show similar magnetic field dependencies, although the magnitude of t he transverse MR is larger than that of the longitudinal MR. For the aged s amples, the rho(T) increase more rapidly upon cooling than that of the fres h samples. The MR of the aged samples is positive. The localization-interac tion theory is examined for the observed rho(T) and MR data of doped PA. Bu t the model of interchain charge transfer bridged by the dopants seems to e xplain the negative MR as well as the metallic temperature dependence of re sistivity for the perchlorate doped polyacetylene. (C) 1999 Elsevier Scienc e S.A. All rights reserved.