Near-field optical spectroscopy of localized and delocalized excitons in a single GaAs quantum wire

Excitons in a GaAs quantum wire are studied in high-resolution photoluminescence experiments performed at a temperature of about 10 K with a spatial resolution of 150 nm, and a spectral resolution of 100 μeV. We report an observation of quasi-one-dimensional excitons which are delocalized over a length of up to several microns along the quantum wire. Such excitons give rise to a 10-meV broad luminescence band, representing a superposition of transitions between different delocalized states. In addition, we find a set of sharp luminescence peaks from excitons localized on a sub-150-nm length scale. Theoretical calculations of exciton states in a disordered quasi-one-dimensional potential reproduce the experimental results.