Quadexciton cascade and fine structure splitting of the triexciton in a single quantum dot

TL;DR

This study investigates the cascade emission and fine structure splitting of quadexcitons in single quantum dots, revealing polarization properties and the influence of anisotropic confinement on energy level splitting.

Contribution

It provides new insights into the polarization correlations and fine structure splitting of quadexcitons, highlighting the relationship with quantum dot size and composition.

Findings

Photon polarization is preserved in the 4X-3X cascade.

Splitting of the triexciton exceeds that of the exciton by up to eight times.

Splitting scales with the energy difference between 3X and X emissions.

Abstract

We report the properties of emission lines associated with the cascaded recombination of a quadexciton in single GaAlAs/AlAs quantum dots, studied by means of polarization-resolved photoluminescence and single-photon correlation experiments. It is found that photons which are emitted in a double-step 4X-3X process preserve their linear polarization, similarly to the case of conserved polarization of correlated photons in the 2X-X cascade. In contrast, an emission of either co-linear or cross-linear pairs of photons is observed for the 3X-2X cascade. Each emission line associated with the quadexciton cascade shows doublet structure in the polarization-resolved photoluminescence experiment. The maximum splitting is seen when the polarization axis is chosen along and perpendicular to the [110] crystallographic direction. This effect is ascribed to the fine structure splitting of the exciton and triexciton states in the presence of an anisotropic confining potential of ae dot. We also show that the splitting in the triexciton state surpasses that in the exciton state by a factor up to eight and their ratio scales with the energy distance between the 3X and X emission lines, thus, very likely, with a lateral size and/or a composition of the dot.