Spin and energy transfer in nanocrystals without transport of charge

TL;DR

This paper introduces a charge-free spin transfer mechanism between quantum dots via Coulomb interaction, enabling efficient energy and spin transfer with potential applications in nanocrystal-based spintronics.

Contribution

It presents a novel Coulomb-mediated spin transfer process in quantum dot pairs that preserves electron spin without charge transport, expanding understanding of spin dynamics in nanocrystals.

Findings

Spin transfer can occur without charge tunneling.

Efficient energy and spin transfer under resonant conditions.

Electron spin orientation can be preserved in randomly-oriented nanocrystals.

Abstract

We describe a mechanism of spin transfer between individual quantum dots that does not require tunneling. Incident circularly-polarized photons create inter-band excitons with non-zero electron spin in the first quantum dot. When the quantum-dot pair is properly designed, this excitation can be transferred to the neighboring dot via the Coulomb interaction with either {\it conservation} or {\it flipping} of the electron spin. The second dot can radiate circularly-polarized photons at lower energy. Selection rules for spin transfer are determined by the resonant conditions and by the strong spin-orbit interaction in the valence band of nanocrystals. Coulomb-induced energy and spin transfer in pairs and chains of dots can become very efficient under resonant conditions. The electron can preserve its spin orientation even in randomly-oriented nanocrystals.