Correlated electrons in optically-tunable quantum dots: Building an electron dimer molecule

TL;DR

This paper investigates the excitations of a two-electron quantum dot molecule, revealing spin and charge modes and linking observed excitations to molecular breathing modes, with tunable electron numbers via optical illumination.

Contribution

It demonstrates optical tuning of electron numbers in quantum dots and links experimental excitations to theoretical models of electron dimers.

Findings

Identification of inter-shell excitations in one-electron regime

Observation of distinct spin and charge modes in two-electron configuration

Determination of singlet-triplet energy splitting

Abstract

We observe the low-lying excitations of a molecular dimer formed by two electrons in a GaAs semiconductor quantum dot in which the number of confined electrons is tuned by optical illumination. By employing inelastic light scattering we identify the inter-shell excitations in the one-electron regime and the distinct spin and charge modes in the interacting few-body configuration. In the case of two electrons a comparison with configuration-interaction calculations allows us to link the observed excitations with the breathing mode of the molecular dimer and to determine the singlet-triplet energy splitting.