METALLIC CONDUCTIVITY AT LOW-TEMPERATURES IN POLY(3,4-ETHYLENEDIOXYTHIOPHENE) DOPED WITH PF6

The temperature dependences of the conductivity and magnetoconductivit y pf poly(3,4-ethylenedioxythiophene) doped with PF6 (room-temperature conductivity of 200-300 S/cm) have been studied; sigma(T) is weakly t emperature dependent with the characteristic resistivity ratio rho(r)= rho(1.4 K)/rho(291 K) =1.5-2.8. The sign of the temperature coefficien t of resistivity (TCR) changes below 10 K from negative to positive fo r metallic samples with rho(r)<2.1; the temperature of the resistivity maximum, T-m, decreases with increasing rho(r). High magnetic fields induce the transition from positive to negative TCR for all samples wi th rho(r)<2.1 and decrease the low-temperature conductivity (negative magnetoconductance) for samples with rho(r) > 2.1. The conductivity at low temperatures is well described by a T-1/2 dependence in both case s (negative and positive TCR) in a magnetic field and with the magneti c field equal to zero. The magnetoconductance is negative, isotropic, and exhibits an H-2 dependence at low magnetic fields and an H-1/2 dep endence at high magnetic fields. These results are successfully explai ned as resulting from the influence of electron-electron interactions on the low-temperature conductivity.