Same Charge Polaron and Bipolaron Scattering on Conducting Polymers

Abstract

We study the dynamics of scattering of two positive polarons moving toward each other with parallel spins and of a polaron and a bipolaron both with positive charges and different velocities, in single chains of cis-polyacetylene and polyparaphenylene. We use the Su-Schrieffer-Heeger model with Hubbard extensions solved within of the time-dependent Hartree-Fock approximation to account for electron-electron interactions, developed over a hexagonal lattice. The main results are elastic scattering in most cases. This behavior changes to transmission of the polaron through the bipolaron when the ratio of their velocities in the same direction is in the range of 3:1 to 5:1 when no external electric field is present. The velocities ratio changes to of 6:1 to 8:1 under external electric field. This suggests that these systems may present an abrupt increase in the charge transport, under specific conditions, in an otherwise smoothly and monotonically increasing relation to the applied field. Their effective masses in these systems are also determined: the polaron effective mass is 4-8 times the rest mass of a free electron, and that of the bipolaron is 15-30 times the electron mass.