Effect of Monolayer Thickness Fluctuations on Coherent Exciton Coupling in Single Quantum Wells

TL;DR

This study investigates how monolayer thickness fluctuations in quantum wells influence the coherent exciton coupling, revealing that disorder type and well width significantly affect coupling strength, measured via advanced spectroscopy.

Contribution

It provides the first combined experimental and theoretical analysis of how different disorder types impact exciton coherence in quantum wells.

Findings

Coherent coupling mainly occurs between excitons in disorder-free regions and plateau-type disorder.

Excitons in fault-type disorder do not exhibit coherent coupling.

Coupling strength varies with quantum well width and disorder type.

Abstract

Monolayer fluctuations in the thickness of a semiconductor quantum well (QW) lead to three types of excitons, located in the narrower, average and thicker regions of the QW, which are clearly resolved in optical spectra. Whether or not these excitons are coherently coupled via Coulomb interactions is a long-standing debate. We demonstrate that different types of disorder in QWs distinctly affects the coherent coupling and that the coupling strength can be quantitatively measured using optical two-dimensional Fourier transform spectroscopy. We prove experimentally and theoretically that in narrow quantum wells the coherent coupling occurs predominantly between excitons residing in the disorder-free areas of the QWs and those residing in the plateau-type disorder. In contrast, excitons localized in the fault-type disorder potentials do not coherently couple to other excitons.