Excitons in quantum dot molecules: Coulomb coupling, spin-orbit effects and phonon-induced line broadening

TL;DR

This paper provides a comprehensive theoretical analysis of excitonic states and optical line shapes in coupled quantum dot molecules, highlighting the effects of Coulomb, spin-orbit, and phonon interactions on spectral features.

Contribution

It introduces a detailed theoretical model that accounts for multiple coupling mechanisms and phonon effects in quantum dot molecules, advancing understanding of their optical properties.

Findings

Coulomb and spin-orbit couplings cause characteristic spectral crossings and avoided crossings.

Phonon interactions significantly broaden optical lines, especially near anticrossings.

Line width enhancement depends strongly on exciton energy splitting.

Abstract

Excitonic states and the line shape of optical transitions in coupled quantum dots (quantum dot molecules) are studied theoretically. For a pair of electrically tunable, vertically aligned quantum dots we investigate the coupling between spatially direct and indirect excitons caused by different mechanisms such as tunnel coupling, Coulomb coupling, coupling due to the spin-orbit interaction and coupling induced by a structural asymmetry. The peculiarities of the different types of couplings are reflected in the appearance of either crossings or avoided crossings between direct and indirect excitons, the latter ones being directly visible in the absorption spectrum. We analyze the influence of the phonon environment on the spectrum by calculating the line shape of the various optical transitions including contributions due to both pure dephasing and phonon-induced transitions between different exciton states. The line width enhancement due to phonon-induced transitions is particularly pronounced in the region of an anticrossing and it strongly depends on the energy splitting between the two exciton branches.