Exciton spin-flip rate in quantum dots determined by a modified local density of optical states

TL;DR

This study measures the exciton spin-flip rate in quantum dots using a modified local density of optical states, revealing effects of interfaces and validating a theoretical model, advancing understanding of quantum dot dynamics.

Contribution

We experimentally determine the exciton spin-flip rate in quantum dots with a novel approach that isolates radiative effects and compares results to existing theoretical models.

Findings

Spin-flip rate depends on emission energy.

Enhanced spin-flip rate near interfaces.

Agreement with a model involving exchange interaction and phonons.

Abstract

The spin-flip rate that couples dark and bright excitons in self-assembled quantum dots is obtained from time-resolved spontaneous emission measurements in a modified local density of optical states. Employing this technique, we can separate effects due to non-radiative recombination and unambiguously record the spin-flip rate. The dependence of the spin-flip rate on emission energy is compared in detail to a recent model from the literature, where the spin flip is due to the combined action of short-range exchange interaction and acoustic phonons. We furthermore observe a surprising enhancement of the spin-flip rate close to a semiconductor-air interface, which illustrates the important role of interfaces for quantum dot based nanophotonic structures. Our work is an important step towards a full understanding of the complex dynamics of quantum dots in nanophotonic structures, such as photonic crystals, and dark excitons are potentially useful for long-lived coherent storage applications.