THE LOCALIZATION-INTERACTION MODEL APPLIED TO THE DIRECT-CURRENT CONDUCTIVITY OF METALLIC CONDUCTING POLYMERS

The low-temperature DC-transport properties of doped conducting polyme rs on the metallic side of the metal-insulator transition are analysed with modern localization-interaction theories. The DC conductivity at the lowest temperatures is governed by the 3D electron-electron inter action formula sigma = sigma(0) + mT(1/2), while the magnetoconductanc e is an interplay between electron-electron interaction and weak-local ization contributions. The transition from negative to positive temper ature coefficient of resistivity, below 20 K, can be explained by the sign change in the interaction coefficient m. On the basis of experime ntal data it is shown that the resistivity ratio rho(r) (rho(r) = rho( T congruent to 1 K)/rho(300 K)) is a controlling factor in determining the sign and magnitude of these effects. Furthermore, the normalizati on of relevant coefficients (e.g. m) with sigma(0) gives the result th at the relative size of the effects is independent of the degree of ch ain orientation, and therefore the conductivity. However, it is found that the coefficient m dresses from negative to positive values at dif ferent values of rho(r), for oriented and non-oriented conducting poly mers. The positive magnetoconductance stemming from weak localization is substantial and very anisotropic in highly oriented conducting poly mers. It is shown that this positive magnetoconductance exhibits a max imum as a function of rho(r), in the vicinity of the metal-insulator t ransition. These results are compared with transport in other types of disordered metal.