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Spin-Dependent Fluorescence Mediated by Antisymmetric Exchange in Triplet Exciton Pairs
Yan Sun1, G Ricci2, M Monteverde1
1Université Paris-Saclay, LPS, CNRS, UMR 8502, F-91405 Orsay, France.
Abstract:
Singlet fission and triplet-triplet annihilation (TTA) are spin-dependent phenomena critical to optoelectronics. The dynamics of spin populations during geminate triplet pair separation are crucial for controlling fission and TTA rates. We show that the Dzyaloshinskii-Moriya interaction (DMI) induces level crossings between spin manifolds, affecting spin populations and TTA rates in crystalline fission semiconductors. By investigating spin-dependent fluorescence in a triplet exciton pair with the magnetic field aligned along the fine structure tensor, we isolate the effect of DMI, as the triplet wave functions remain unaffected by the field. Our results reveal that DMI introduces additional TTA pathways that are forbidden by spin conservation, explaining the observed evolution of optically detected magnetic resonance signals with varying magnetic field. The magnitude of the DMI interactions needed to reproduce the experimental data is further confirmed by highly correlated wave function-based ab initio calculations. This Letter highlights the significant impact of DMI on the optical properties of triplet excitons, advancing our understanding of spin dynamics in these systems.
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