Asymmetry in self-assembled quantum dot-molecules made of identical InAs/GaAs quantum dots

TL;DR

This paper investigates the asymmetry in wavefunctions of identical InAs/GaAs quantum dot molecules, revealing how strain and electron correlation induce localization and affect energy splitting.

Contribution

It demonstrates the origin of asymmetry in wavefunctions and quantifies singlet-triplet splitting in identical quantum dot molecules, a novel insight into their electronic structure.

Findings

Asymmetry in single-particle wavefunctions due to strain.

Correlation-induced localization of electrons in the molecule.

Large singlet-triplet energy splitting compared to larger dots.

Abstract

We show that a diatomic dot molecule made of two identical, vertically stacked, strained InAs/GaAs self-assembled dots exhibits an asymmetry in its single-particle and may-particle wavefunctions. The single-particle wave function is asymmetric due to the inhomogeneous strain, while the asymmetry of the many-particle wavefunctions is caused by the correlation induced localization: the lowest singlet $^1\Sigma_g$ and triplet $^3\Sigma$ states show that the two electrons are each localized on different dots within the molecule, for the next singlet states $^1\Sigma_u$ both electrons are localized on the same (bottom) dot for interdot separation $d>$ 8 nm. The singlet-triplet splitting is found to be $\sim 0.1$ meV at inter-dot separation $d$=9 nm and as large as 100 meV for $d$=4 nm, orders of magnitude larger than the few meV found in the large (50 - 100 nm) electrostatically confined dots.