Microscopic origin of the effective spin-spin interaction in a semiconductor quantum dot ensemble

TL;DR

This paper develops a microscopic model to explain the origin of long-range effective spin-spin interactions in semiconductor quantum dot ensembles, revealing an antiferromagnetic coupling at short distances and matching experimental spin dynamics.

Contribution

It introduces a microscopic understanding of the spin-spin interaction mediated by wetting layers, using NRG calculations and semiclassical simulations to match experimental observations.

Findings

Antiferromagnetic Heisenberg coupling at short inter-dot distances

Effective interaction mediated by wetting layer band asymmetry

Reproduction of experimental phase shifts in spin dynamics

Abstract

We present a microscopic model for a singly charged quantum dot (QD) ensemble to reveal the origin of the long-range effective interaction between the electron spins in the QDs. Wilson's numerical renormalization group (NRG) is used to calculate the magnitude and the spatial dependency of the effective spin-spin interaction mediated by the growth induced wetting layer. Surprisingly, we found an antiferromagnetic Heisenberg coupling for very short inter-QD distances that is caused by the significant particle-hole asymmetry of the wetting layer band at very low filling. Using the NRG results obtained from realistic parameters as input for a semiclassical simulation for a large QD ensemble, we demonstrate that the experimentally reported phase shifts in the coherent spin dynamics between single and two color laser pumping can be reproduced by our model, solving a longstanding mystery of the microscopic origin of the inter QD electron spin-spin interaction.