Spin dependent fluorescence mediated by anti-symmetric exchange in triplet exciton pairs

TL;DR

This study demonstrates how the Dzyaloshinskii-Moriya interaction influences spin populations and fluorescence in triplet exciton pairs, revealing new pathways for triplet-triplet annihilation in optoelectronic materials.

Contribution

It uncovers the role of DMI in modulating spin dynamics and fluorescence in triplet exciton pairs, a novel insight into spin-dependent processes in fission semiconductors.

Findings

DMI causes level crossings between spin states affecting TTA rates.

DMI introduces forbidden TTA pathways, altering optical signals.

Magnetic field alignment isolates DMI effects on triplet wavefunctions.

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 wavefunctions 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. This study highlights the significant impact of DMI on the optical properties of triplet excitons, advancing our understanding of spin dynamics in these systems.