Ch. Lienau, F. Intonti, V. Emiliani, T. Guenther, and T. Elsaesser

We discuss high-resolution photoluminescence spectra of single quantum wires and thin quantum wells that are recorded by near-field spectroscopy with a spatial resolution of 150 nm and a spectral resolution of 100 meV. In such disordered quantum systems, localized exciton states play a key role for the optical and transport properties. The disorder-induced broken translational symmetry of the nanostructure leads to slightly different exciton eigen and thus optical transition energies. This gives rise to inhomoegneously broadened far-field optical spectra. On the other hand, in highly spatially and spectrally resolved experiements the smooth inhomogeneously broadened line of macroscopic PL spectra breaks up into many narrow spikes from single localized excitons whose individual spectral widths are often determined by experimental resolution or by the natural line width.

In experiments on single quantum wires, we demonstrate that the localization length of the different excitonic eigenstates in such disorder systems may vary over a wide range between typically 10 nm up several mm. The optical signatures of these excitonic states in high spectral resolution near-field images will be shown to be clearly different, a behavior that is well accounted for by theoretical calculations of exciton states in a disorder potential [1].

Experiments on single thin quantum wells demonstrate that the statistical properties of the different localized exciton states bear precise information about the nature of the underlying disorder potential, specifically its correlation length. We subject a set of several hundred near-field spectra displaying sharp emission lines to an analysis of the two-energyautocorrelation function [2]. An accurate comparison with a quantum theory of the exciton center-of-mass motion in a two-dimensional spatially-correlated disordered potential reveals clear signatures of quantum-mechanical energy level repulsion, giving the spatial and energetic correlations of excitons in disordered quantum systems.

[1] F. Intonti, V. Emiliani, C. Lienau, T. Elsaesser, R. Noetzel, and K. H. Ploog, Phys. Rev. B, in press (2001).

[2] F. Intonti, V. Emiliani, C. Lienau, T. Elsaesser, V. Savona, E. Runge, R. Zimmermann, R. Noetzel, and K. H. Ploog, submitted.