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arXiv · 2208.07505

Unified definition of exciton coherence length for exciton-phonon coupled molecular aggregates

Tong Jiang·Jiajun Ren·Zhigang Shuai
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Abstract

Exciton coherence length (ECL) is an essential concept to characterize the nature of exciton in molecular aggregates for photosynthesis, organic photovoltaics, and light-emitting diodes. ECL has been defined in a number of ways through the variance or purity of the electronic reduced density matrix. However, we find that these definitions fail to present a monotonic relationship with respect to the exciton radiative decay efficiency as it should be when exciton-phonon couplings are taken into accounts. We propose a unified definition of ECL by virtue of sum rule of oscillator strengths. Using the numerically accurate time-dependent matrix product states formalism applied to Frenkel-Holstein models for molecular aggregates in both one- and two-dimensional system, we find our ECL definition exhibits a monotonic relationship with respect to the radiative efficiency and can serve as an efficient and unified description for exciton coherence. We further predict that the two-dimensional aggregates can display maximum superradiance enhancement (SRE) at finite temperature, different from the previous knowledge of SRE-$1/T$ behavior.

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Tong Jiang, Jiajun Ren, Zhigang Shuai. 2022-08-16. Unified definition of exciton coherence length for exciton-phonon coupled molecular aggregates. https://arxiv.org/abs/2208.07505

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