Excitons in quasi-one dimensional organics: Strong correlation approximation
arXiv:cond-mat/9709254 · doi:10.1103/PhysRevB.56.3697
Abstract
An exciton theory for quasi-one dimensional organic materials is developed in the framework of the Su-Schrieffer-Heeger Hamiltonian augmented by short range extended Hubbard interactions. Within a strong electron-electron correlation approximation, the exciton properties are extensively studied. Using scattering theory, we analytically obtain the exciton energy and wavefunction and derive a criterion for the existence of a exciton. We also systematically investigate the effect of impurities on the coherent motion of an exciton. The coherence is measured by a suitably defined electron-hole correlation function. It is shown that, for impurities with an on-site potential, a crossover behavior will occur if the impurity strength is comparable to the bandwidth of the exciton, corresponding to exciton localization. For a charged impurity with a spatially extended potential, in addition to localization the exciton will dissociate into an uncorrelated electron-hole pair when the impurity is sufficiently strong to overcome the Coulomb interaction which binds the electron-hole pair. Interchain coupling effects are also discussed by considering two polymer chains coupled through nearest-neighbor interchain hopping and interchain Coulomb interaction . Within the matrix scattering formalism, for every center-of-mass momentum, we find two poles determined only by , which correspond to the interchain excitons. Finally, the exciton state is used to study the charge transfer from a polymer chain to an adjacent dopant molecule.
24 pages, 23 eps figures, pdf file of the paper available