Spin and energy transfer in nanocrystals without tunneling

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Abstract
We describe a mechanism of spin transfer between individual quantum dots without tunneling. Incident circularly polarized photons create interband excitons with nonzero 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 conservation or flipping of electron spin. The second dot can radiate circularly polarized photons at smaller 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.