Negative exchange interactions in coupled few-electron quantum dots

TL;DR

This paper demonstrates through microscopic modeling that negative exchange interactions in coupled quantum dots can occur with few electrons, challenging the notion that large electron numbers are necessary for such effects.

Contribution

It provides a detailed microscopic analysis showing negative exchange interactions can arise in few-electron quantum dots, not just large electron systems.

Findings

Negative exchange interactions occur in few-electron quantum dots.

Triplet-like ground states are possible with as few as four electrons.

Negative exchange interactions are robust across different materials and geometries.

Abstract

It has been experimentally shown that negative exchange interactions can arise in a linear three-dot system when a two-electron double quantum dot is exchange coupled to a larger quantum dot containing on the order of one hundred electrons. The origin of this negative exchange can be traced to the larger quantum dot exhibiting a spin triplet-like rather than singlet-like ground state. Here, we show using a microscopic model based on the configuration interaction (CI) method that both triplet-like and singlet-like ground states are realized depending on the number of electrons. In the case of only four electrons, a full CI calculation reveals that triplet-like ground states occur for sufficiently large dots. These results hold for symmetric and asymmetric quantum dots in both Si and GaAs, showing that negative exchange interactions are robust in few-electron double quantum dots and do not require large numbers of electrons.