Influence of Many-Body Effects on the Quantum Coherence of 2D Excitons in GaAs Quantum Wells

Abstract

The polarization dependence of time-integrated (TI) and time-resolved (TR) degenerate four-wave-mixing (DFWM) on the lowest heavy hole (hh) and light hole (lh) exciton transitions in GaAs quantum wells (QW) demonstrates that heavy and light hole excitons cannot be described in the framework of the two non-interacting three-level systems with opposite circular polarization selection rules suggested by Schmitt-Rink et al.1 In several recent papers, 2–5 we have shown that the discrepancies between experiment and theory can be resolved if many-body Coulomb interactions and disorder-induced coupling of excitonic states are taken into account. Exciton/exciton Coulomb interaction which involves a variation of the local electric fields (LFE), excitation-induced dephasing (EID) and energy shifts of excitonic states, especially the formation of biexcitons (BIF), is phenomenologically implemented into the theory by solving the optical Bloch equations for multi-level model systems which represent single-exciton and two-exciton contributions to the nonlinear optical response by discrete transitions with adjustable oscillator strengths, dephasing rates, and frequencies. Comparison of a large variety of experimental data with theoretical curves calculated with this model demonstrates, in particular, the important contribution of the heavy hole biexciton to the third-order nonlinear optical response of GaAs QW’s. Whereas modulation of the signal with a frequency corresponding to the biexciton binding energy are the unique “fingerprint” for the formation of biexcitons, their importance is further proved by the polarization dependence of the signal strength.