IMPURITY-INDUCED DEFECT STATES IN POLYACETYLENE

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Abstract
The effect of impurities on both the electronic structure and the lattice distortions in polyacetylene is studied using the SSH Hamiltonian and an impurity potential acting on a single site. Assuming an ideally dimerized chain it is shown that the impurities lead to localized electronic states with energy levels tending to mid-gap and extents approaching the characteristic soliton length with increasing strength of the impurity potential. Both the discrete and the continuum model yield the same result in the weak-coupling limit. The impurity-induced optical absorption is calculated and found to be weaker by a factor of about 4 than the soliton-induced absorption. Finally the modifications in the electronic structure are shown to lead to strong lattice relaxation, and it is concluded that the impurities affect both the electronic states and the displacement pattern of the lattice

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