Dephasing in the quasi-two-dimensional exciton-biexciton system

Abstract

The polarization decay in the exciton-biexciton system of a homogeneously broadened single quantum well is studied by transient four-wave mixing. All three decay rates in the exciton-biexciton three-level system are deduced. The relation between the rates unravels correlations between scattering processes of excitons and biexcitons. Density and temperature dependences show that the involved processes are mainly radiative decay and phonon scattering. The radiative decay rate of the biexcitons is found to be comparable to the one of the excitons, and the involved spontaneous photon emissions from excitons and biexcitons are mutually uncorrelated. In contrast, the biexciton phonon scattering is twice as fast and correlated to exciton-phonon scattering, indicating the interaction with similar phonon modes. The enhancement of the Coulomb interaction between electrons and holes in semiconductor nanostructures leads to pronounced excitonic effects. This gives a strong influence on the optical nonlinearity not only from excitons but also from biexcitons. The binding energy of the biexcitons has been investigated in great detail, 1‐3 while only little is known about the scattering processes of biexcitons 4‐6 compared to that of excitons. 7 In four-wave mixing ~FWM! spectroscopy, commonly used to measure scattering processes, the disorder present in nanostructures strongly modifies the FWM response, 8 especially the biexcitonic signal, 9,10 and the analysis of the biexciton scattering is intricate. 11 In a homogeneously broadened system instead, the dephasing rates of exciton and biexciton to ground-state transitions and also of the exciton-biexciton transition can be determined. This gives the opportunity to analyze not only the biexciton scattering processes but also their correlation with the exciton scattering processes, providing insight into the microscopic dynamics of the involved scattering events. A prominent example of a strong correlation of such scattering events is a slow dephasing of intraband coherences created by interband transitions of fast dephasing, like heavy-hole‐light-hole