Exchange energy and stability diagram of few-electron coupled elongated quantum dots

TL;DR

This paper investigates how the exchange energy and stability of few-electron elongated quantum dots change with aspect ratio, revealing a sharp transition at a specific ratio and effects on electron localization and spin states.

Contribution

It introduces a detailed analysis of exchange energy variation and stability regions in elongated coupled quantum dots using exact diagonalization, highlighting a critical aspect ratio effect.

Findings

Exchange energy sharply varies at aspect ratio 3.9

Stability region with one electron per dot shrinks and vanishes

First singlet-triplet transition shifts to small magnetic fields for r>3.9

Abstract

We study the properties of a few-electron system confined in coupled elongated quantum dots (QDs) using a model Gaussian potential and the numerical exact diagonalization technique. In the absence of magnetic fields, as the aspect ratio $r$ between the QD extensions in the direction perpendicular and parallel to the coupling directions increases, the exchange energy exhibits a sharp variation at the specific value $r=3.9$, before (after) which the exchange energy increases (declines). The sharp variation occurs because of a sudden change in the single-particle configuration of the triplet state. The stability region with one electron in each of the QDs is found to shrink, and finally vanishes as it becomes progressively easier to localize both electrons into the lower QD. For $r>3.9$, the first singlet-triplet transition shifts to a small magnetic fields.