The linear response of biexciton to external electrical field in polymer

In external electrical field, the self-trapping biexciton in non-degenerate ground state conjugated polymer has an abnormal characteristic-its static polarizability was found to be negative. We calculated the dynamic response function chi(omega) of biexciton. By putting omega to the zero limit, we g ot the static polarizability chi which proved to be negative. We compared i t with that of self-trapping exciton and ground state and gave some analysi s on the origin of negative polarizability. Finally, we investigated the be havior of chi(omega) when omega is small, and deduced that if more biexcito ns are excited, the n(omega) of the material will decrease, whereas if more excitons are excited, the n(omega) will increase.