The effects of pressure and magnetic field on the conductivity of FeCl₄ doped polyacetylene: The influence of scattering by low-energy excitations

The effects of hydrostatic pressure and magnetic field on the conductivity of oriented polyacetylene films doped with FeC1₄- up to metallic state have been studied at T = 0.35-300 K. It was found that application of pressure up to 10 kBar increases the conductivity at 300 K by a factor of 1.3 and suppresses the resistivity minimum in ρ(T) at 270 - 280 K. At T < 2 K the temperature dependence of resistivity ρ(T) ∼ In T (at ambient pressure and at 10 kBar) which remains unaltered by a magnetic field up to 14 Tesla. Transverse magnetoresistance (MR) was found to be negative, linear and temperature independent at T < 2 K (at ambient and high pressure). We attribute the observed ρ(T) and MR behavior to weak localization accompanied by effect of electron dephasing time saturation due to scattering by two-level systems of a special type. More strong behavior of ρ(T) and MR at T > 2 K related to further suppression of weak localization due to scattering by low-energy excitations of a "glassy" type.