Optical transitions, exciton radiative decay, and valley coherence in lead chalcogenide quantum dots

TL;DR

This paper introduces the concepts of valley coherence and superradiance in reciprocal space, explaining their impact on exciton radiative decay in lead chalcogenide quantum dots and addressing observed long lifetimes.

Contribution

It proposes the novel ideas of valley coherence and superradiance in reciprocal space and explains their effects on exciton radiative decay in lead chalcogenide quantum dots.

Findings

Valley coherence and superradiance lead to an N-fold decrease in exciton radiative lifetime.

Despite this, measured lifetimes are in the microsecond range due to material properties.

Light-matter interaction in narrow-gap materials exhibits unique features.

Abstract

We propose the concept of valley coherence and superradiance in the reciprocal space and show that it leads to an $N$-fold decrease of the bright exciton radiative lifetime in quantum dots (QDs) of an $N$-valley semiconductor. Next we explain why, despite this, the exciton radiative lifetimes in PbX (X = S, Se, Te) QDs, measured from the photoluminescence decay, are in the microsecond range. We also address peculiarities of the light-matter interaction in nanostructures made of narrow-gap materials with strong inter-band coupling.