ELECTRICAL TRANSPORT IN DOPED POLYPYRROLE FILMS AT LOW-TEMPERATURE

We report the results of a comprehensive study of localization and electron-electron interaction effects in doped polypyrrole films. We have measured the electrical conductivity and magnetoconductivity within the temperature range 1.8 K less-than-or-equal-to T less-than-or-equal-to 300 K. The observed temperature dependence of dc conductivity cannot be explained either by the band-conduction model or by assuming a temperature-dependent energy gap. However, the conductivity when temperature T > 10 K can be explained by Mott's variable-range hopping model and the density of states and hopping distance can be calculated from these data. The low-temperature conductivity obeys a T1/2 law, which is explained by three-dimensional localization and an electron-electron interaction. Magnetoconductivity data indicate that the electron-electron-interaction effect is most prominent in doped polypyrrole films at low temperature. From the magnetoconductivity we have calculated the inelastic and spin-orbit-scattering time. The spin-orbit scattering is found to be independent of temperature and small in comparison with the inelastic scattering. Like three-dimensional amorphous metals the inelastic scattering field obeys a T(p) (p almost-equal-to 2) law at low temperature.