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physica status solidi (b)

Coherent nonlinear optical response of excitons and biexcitons in quantum dots coupled to phonons

A. Krügel, V. M. Axt, T. Kühn, Alexei Vagov, François Maria Peeters

Published Jul 27, 2006• 2 citations
Publisher

Abstract

Abstract Four wave mixing signals from single dots and dot ensembles involving excitonic and biexcitonic transitions are discussed. The results have been obtained analytically from a four level dot model coupled to longitudinal acoustic phonons. Time integrated four wave mixing amplitudes for quantum dot ensembles exhibit polarization dependent quantum beats that have already been found in experimental data. In four wave mixing signals of single quantum dots we find that the ground state to exciton transition has two contributions. One is identical to the known solution of the two level quantum dot model and leads to symmetric spectra for longer delay times, while the other comprises phase information from the biexciton and results in asymmetric spectra. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI
10.1002/pssb.200668034

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We report time-resolved degenerate four-wave-mixing experiments on a high-quality single GaAs quantum well. The signals for parallel and cross-polarized exciting pulses show pronounced quantum beats with different frequencies corresponding to the heavy/light-hole splitting and the biexciton binding energy, respectively. Comparison of the experimental data with solutions of the optical Bloch equations for a phenomenological model system shows that these features result from strong contributions of the biexcitonic state. The importance of biexcitons to the nonlinear coherent response of the two-dimension exciton is further confirmed by the frequency dependence of the time-integrated four-wave-mixing signal amplitudes measured for the two polarization geometries.