Helical polyacetylene heavily doped with iodine: Magnetotransport

The magnetoconductivity of two kinds of iodine doped helical polyacetylene, R- and S-polyacetylene, were investigated to understand the effect of the intrafibril and the interfibrillar interaction in the polyacetylene system. The zero-field resistivity ratio, rho (r)=rho (1.2 K)/rho (300 K), is comparable to that of stretch-oriented high-density polyacetylene film, which indicates the partial alignment of chains inside a polymer fiber. At low magnetic fields, the small negative component of magnetoconductivity (positive magnetoresistance) was observed and its magnitude increases as the rho (r) value increases. In the high field region, the magnetoconductivity is positive and it clearly shows the linear dependence on the magnetic field up to H=30 T. The linear field dependence of magnetoconductivity is different from what is expected in the three-dimensional localization-interaction picture. For the same rho (r) value samples, the magnitude of negative magnetoconductivity of S-polyacetylene is much bigger than that of R-polyacetylene, which could be attributed to the difference in the degree of helicity determining the strength of interfibrillar interaction. (C) 2001 American Institute of Physics.