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

The effects of hydrostatic pressure and magnetic field on the low-temperature conductivity of oriented polyacetylene doped with FeCl₄^- up to a metallic state have been investigated. It was found that the conductivity at 10 kbar is greater than that at ambient pressure by a factor of 1.3. Application of pressure suppresses the resistivity minimum at 280 K and decreases the resistivity ratio ρ_r=ρ(0.37 K)/ρ(300 K) from 2.4 down to 1.9. The temperature dependence of resistivity ρ(T)∼InT at temperatures below 1 K at ambient pressure and at 10 kbar, which remains almost unaltered by a magnetic field up to 14 T. The starting temperature of the logarithmic temperature dependence shifts by a magnetic field up to higher temperatures. Transverse magnetoresistance (MR) was found to be negative, linear, and almost temperature-independent at temperatures below 2 K. The low temperature ρ(T) and MR behavior at T<1 K observed in heavily doped polyacetylene has been attributed to weak localization. We assumed that a dramatic increase of inelastic scattering due to low-energy vibrational excitation can ascribe the stronger temperature behavior of ρ(T) and MR at T>2 K as a result of further suppression of weak localization due to a more effective dephasing effect. At higher temperature, the resistivity decrease is dominated by activation to additional conduction paths.