Metallic conductivity at low temperatures in poly(3,4-ethylenedioxythiophene) doped withPF6

The temperature dependences of the conductivity and magnetoconductivity of poly(3,4-ethylenedioxythiophene) doped with ${\mathrm{PF}}_6$ (room-temperature conductivity of 200–300 S/cm) have been studied; $\sigma \mathrm{}\left(T\right)\mathrm{}$ is weakly temperature dependent with the characteristic resistivity ratio ${\rho }_r$=ρ(1.4 K)/ρ(291 K)=1.5–2.8. The sign of the temperature coefficient of resistivity (TCR) changes below 10 K from negative to positive for metallic samples with ${\rho }_r<2.1\mathrm{}$; 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 with ${\rho }_r<2.1\mathrm{}$ and decrease the low-temperature conductivity (negative magnetoconductance) for samples with ${\rho }_r>2.1\mathrm{}$. The conductivity at low temperatures is well described by a $T^{1/2}$ dependence in both cases (negative and positive TCR) in a magnetic field and with the magnetic field equal to zero. The magnetoconductance is negative, isotropic, and exhibits an $H^2$ dependence at low magnetic fields and an $H^{1/2}$ dependence at high magnetic fields. These results are successfully explained as resulting from the influence of electron-electron interactions on the low-temperature conductivity.