Optical measurement and modeling of interactions between two hole or two electron spins in coupled InAs quantum dots

TL;DR

This study uses optical spectroscopy to compare exchange interactions between two holes and two electrons in coupled InAs quantum dots, revealing that while both are approximately isotropic, holes exhibit significantly larger asymmetric contributions due to spin-orbit and Zeeman effects.

Contribution

First experimental comparison of exchange interactions in coupled quantum dots for both holes and electrons, highlighting larger asymmetries in hole systems.

Findings

Exchange is approximately isotropic for both holes and electrons.

Asymmetric contributions are larger for holes than electrons.

Significant spin-orbit and Zeeman effects influence the spectra.

Abstract

Two electron spins in quantum dots coupled through coherent tunneling are generally acknowledged to approximately obey Heisenberg isotropic exchange. This has not been established for two holes. Here we measure the spectra of two holes and of two electrons in two vertically stacked self-assembled InAs quantum dots using optical spectroscopy as a function of electric and magnetic fields. We find that the exchange is approximately isotropic for both systems, but that significant asymmetric contributions, arising from spin-orbit and Zeeman interactions combined with spatial asymmetries, are required to explain large anticrossings and fine-structure energy splittings in the spectra. Asymmetric contributions to the isotropic Hamiltonian for electrons are of the order of a few percent while those for holes are an order of magnitude larger.