Competition between polarons and bipolarons — doping and electric field dynamical effects

The dynamics of polarons and bipolarons is numerically studied using the Su-Schrieffer-Heeger model combined with the Pariser-Parr-Pople model extended to include an external electric field and a Brazovskii-Kirova (BK) symmetry breaking interaction. The time-dependent unrestricted Hartree-Fock approximation is used. It is found that dynamical effects do not reverse the stability relation between polarons and bipolarons. On the other hand, as the electric field intensity gets stronger the moving polarons structure is blurred (destroyed) faster than the structure of moving bipolarons. This effect is reduced with increasing doping concentration. Therefore, it is shown within the present model that the applied external electric field as well as the doping concentration are fundamental in determining the relative prevalence of polarons or bipolarons.