Vertically-coupled dipolar exciton molecules

TL;DR

This paper predicts the existence of vertically coupled dipolar exciton molecules in layered semiconductor structures, demonstrating their binding energies and potential for novel collective effects and correlations.

Contribution

It introduces the concept of bound states of dipolar excitons across layers, supported by calculations showing their stability and properties.

Findings

Bound states of excitons across layers are theoretically confirmed.

Binding energy varies with layer separation.

Potential for observing these molecules in real heterostructures.

Abstract

While the interaction potential between two dipoles residing in a single plane is repulsive, in a system of two vertically adjacent layers of dipoles it changes from repulsive interaction in the long range to attractive interaction in the short range. Here we show that for dipolar excitons in semiconductor heterostructures, such a potential may give rise to bound states if two such excitons are excited in two separate layers, leading to the formation of vertically coupled dipolar exciton molecules. Our calculations prove the existence of such bound states and predict their binding energy as a function of the layers separation as well as their thermal distributions. We show that these molecules should be observed in realistic systems such as semiconductor coupled quantum well structures and the more recent van-der-Waals bound heterostructures. Formation of such molecules can lead to new effects such as a collective dipolar drag between layers and new forms of multi-particle correlations, as well as to the study of dipolar molecular dynamics in a controlled system.