Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.023
Publication date: 16th December 2024
Colloidal coupled quantum dots molecules (CQDMs) were recently synthesized by “nano-chemistry”.[1-3] These CQDMs, made by fusing two CdSe/CdS core/shell quantum dots, uniquely consist of two coupled emitting centers. Such CQDMs raise significant fundamental interest as they manifest optical properties differing from those of the constituent quantum dots, which has been taken as a signature of electronic coupling, akin to that in molecules constructed from real atoms.
Recent theoretical studies, however, indicate that the distinct behavior of CQDMs arises mainly from relaxed exciton confinement, rather than molecular-like electronic coupling.[4] The reason is that CQDMs are designed to favor electron tunneling between the dots, but holes remain strongly localized inside the core of the individual dots. Consequently, upon photoexcitation, holes capture electrons and prevent them from tunnel-coupling. The same holds when CQDMs are populated with biexcitons (forming an artificial H2 molecule).[5]
Herein, we present a strategy to restore electronic coupling in CQDMs. By means of k·p simulations, we show that using trions (charged excitons) instead of neutral excitonic complexes, the ground state of the CQDM acquires strong molecular (bonding) character. This is because uncompensated Coulomb repulsions prevent carriers from localizing in individual dots. Positive trions (an artificial H2+ molecule) are found to be particularly apt for the practical realization of CQDMs with substantial electronic coupling.
J.I. and J.P. acknowledge support from Grant No. PID2021-128659NB-I00, funded by Ministerio de Ciencia e Innovaci\'{o}n (MCIN/AEI/10.13039/501100011033 and ERDF A way of making Europe).
J.L acknowledges IKUR Strategy under the collaboration agreement between Ikerbasque Foundation, BCMaterials and Donostia International Physics Center (DIPC)
on behalf of the Department of Education of the Basque Government.
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