Phonon-induced Exciton Dephasing in Quantum Dot Molecules

TL;DR

This paper introduces a microscopic approach to analyze exciton dephasing in quantum dot molecules, considering phonon interactions and their effects on optical properties, including broadening of spectral lines.

Contribution

A generalized cumulant expansion method for multilevel systems is developed to study exciton-phonon interactions in quantum dot molecules.

Findings

Real phonon-assisted transitions dominate dephasing at certain dot distances.

Virtual transitions have minor impact on exciton dephasing.

Coulomb interaction, tunneling, and asymmetry significantly influence dephasing.

Abstract

A new microscopic approach to the optical transitions in quantum dots and quantum dot molecules, which accounts for both diagonal and non-diagonal exciton-phonon interaction, is developed. The cumulant expansion of the linear polarization is generalized to a multilevel system and is applied to calculation of the full time dependence of the polarization and the absorption spectrum. In particular, the broadening of zero-phonon lines is evaluated directly. It is found that in some range of the dot distance real phonon-assisted transitions between exciton states dominate the dephasing, while virtual transitions are of minor importance. The influence of Coulomb interaction, tunneling, and structural asymmetry on the exciton dephasing in quantum dot molecules is analyzed.