Bound Excitons in Sr$_{2}$CuO$_{3}$

TL;DR

This study explores the temperature-dependent optical spectra of Sr$_{2}$CuO$_{3}$, revealing evidence of bound excitons influenced by long-range Coulomb interactions, contrary to previous beliefs based on the extended Hubbard model.

Contribution

The paper provides experimental evidence of bound excitons in a one-dimensional chain compound, highlighting the role of long-range Coulomb interactions in their formation.

Findings

Observation of a blue shift in the charge transfer peak at low temperature.

Detection of sharp peaks at the optical gap indicating excitons.

Confirmation that long-range Coulomb interactions enable exciton formation in 1D systems.

Abstract

We investigated temperature dependent optical spectra of the one-dimensional chain compound Sr$_{2}$CuO$_{3}$. 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.