The persistence of spin coherence in a crystalline environment

TL;DR

This paper investigates how transport-induced dephasing affects quantum interference in triplet excitons within a crystalline environment, combining theoretical modeling with experiments on rubrene crystals to understand entanglement persistence and suppression of quantum beats.

Contribution

It introduces transport-induced dephasing as a key factor in triplet exciton coherence loss and provides experimental validation and parameter estimation in rubrene crystals.

Findings

Triplet pairs remain entangled for over 50 ns.

Quantum beats are suppressed within a few nanoseconds due to TID.

Triplet-exciton hopping rate in rubrene is approximately 150 ps.

Abstract

We analyze quantum interference in the triplet-exciton pair generated by singlet exciton fission in a molecular crystal, and introduce transport-induced dephasing (TID) as a key effect that can suppress the expected fluorescence quantum beats when the triplet-exciton wavefunction can localize on inequivalent sites. TID depends on the triplet-exciton hopping rate between inequivalent sites and on the energy-shifts among the stationary states of the entangled triplet pair in different spatial configurations. The theoretical model is confirmed by experiments in rubrene single crystals, where triplet pairs remain entangled for more than 50 ns but quantum beats are suppressed by TID within a few nanoseconds when the magnetic field is misaligned by just a few degrees from specific symmetric directions. Our experiments deliver the zero-field parameters for the rubrene molecule in its orthorhombic lattice and information on triplet-exciton transport, in particular the triplet-exciton hopping rate between inequivalent sites, which we evaluate to be of the order of 150 ps in rubrene.