Femtosecond dynamics of mixed gap states in conducting polymers

We numerically apply a femtosecond electric pump pulse to a bond-disordered polymer chain in the Su-Schrieffer-Heeger model and observe the formation of localized excitations, particularly bound and separate soliton pairs with a partial occupation of the gap states. Mixed gap states are also found in the mean field dynamics of an electron hole-pair. They are significant optical excitations in conjugated polymers. The ground state of a chain with mixed gap states shows a discontinuous phase transition from bound to separate soliton pairs. We investigate their dynamics under the influence of a dc pump pulse as well as from initial electron hole-pair excitation using ‘mean field’ instead of the often applied ‘adiabatic’ dynamics.