EFFECT OF ANISOTROPY ON CONDUCTIVITY AND MAGNETOCONDUCTANCE IN HEAVILY-DOPED POLYACETYLENE

The conductivity of iodine doped Shirakawa polyacetylene films with va rious stretching ratio (l/l(0) = 1 similar to-6) was measured as a fun ction of temperature, pressure and magnetic field. Unoriented samples show a power-law temperature dependence of the conductivity, with the characteristic resistivity ratio rho(r) = rho(1.4K)/rho(300K) similar to 80, and a positive magnetoresistance at low temperature. Although t he conductivity anisotropy (sigma(parallel to)/sigma(perpendicular to) ) increases with stretching up to sigma(parallel to)/sigma(perpendicul ar to) similar to 110 for l/l(0) = 6, the temperature dependence of th e conductivity (rho(r) = 3.0 +/- 0.3) for stretched sample is nearly i ndependent on the direction and the ratio of stretching. The negative magnetoresistance for the stretched sample indicates that weak localiz ation contribution to the conductivity is dominant at low temperature. The anisotropy of magnetoconductance is close to the conductivity ani sotropy implying that the bulk anisotropy originates from partially al igned fibrillar morphology. Application of high pressure decreases rho (r) and changes the dominant dephasing mechanism of weak localization from the inelastic electron-electron scattering in the dirty limit to that in clean limit.