Polyaniline is a random-dimer model: A new transport mechanism for conducting polymers

We consider here a single randomly protonated strand of the conducting polymer polyaniline and show explicitly that the disorder inherent in this system is described by the random-dimer model of Dunlap, Wu, and Phillips [Phys. Rev. Lett. 65, 88 (1990)] with off-diagonal disorder. We demonstrate exactly that the location in the energy band of the unscattered or conducting states of this model coincides with recent calculations of the location of the Fermi level in the protonated form of the polymer. We argue then that the random-dimer model is capable of explaining the insulator-metal transition in polyaniline.