We investigated temperature dependent optical spectra of the one-dimensional chain compound Sr2CuO3. The charge transfer transition polarized along the chain direction shows a strongly asymmetric line shape as expected in one-dimensional extended Hubbard model. At low temperature the charge transfer peak shows a large blue shift and reveals additional sharp peaks at the gap. Even though many spectroscopic studies suggest that this material can not have a bound exciton based on the one-dimensional extended Hubbard model, we attribute the additional sharp peaks to excitons, which come to exist due to the long range Coulomb interaction.
@article{arxiv.0806.2083,
title = {Bound Excitons in Sr$_{2}$CuO$_{3}$},
author = {K. W. Kim and G. D. Gu and C. C. Homes and T. W. Noh},
journal= {arXiv preprint arXiv:0806.2083},
year = {2009}
}