Probing excitonic nonlinearities in quantum wires

We report on the experimental observation of excitonic molecules (biexciton s) in high-quality V-shaped quantum wires. By means of spatially resolved n ear-field photoluminescence spectroscopy, first we unambiguously isolate ex citons with a one-dimensional character, and secondly we present the optica l transition from 1D biexciton to 1D exciton as a function of excitation po wer density. The density of these biexcitonic molecules is shown to increas e superlinearly compared to the linear variation of exciton density.