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Exciton-Exciton and Exciton-Photon Annihilation in Polaritonic Systems

Strong light--matter interactions forming hybrid quasiparticles termed polaritons can specifically tailor molecular photophysics. In this spirit, enhancing energy transport has recently been of special interest. Exciton--exciton annihilation is commonly used to quantify energy transfer in excitonic systems, and has been recently applied to investigate transport dynamics in polaritonic systems. However, the interpretation of experimental findings is challenging without a microscopic theory that accounts for the various nonradiative relaxation channels determining the quasiparticle diffusion length. In this work, we develop a microscopic model for polariton annihilation based on exciton--exciton annihilation and propose an exciton--photon annihilation as the decisive process that competes with exciton--exciton annihilation. The interplay between exciton--exciton and exciton--photon annihilation ultimately governs the annihilation dynamics and sets the fundamental limit to the transport efficiency. Our model explains recent experimental results and demonstrates that increased annihilation rates might serve as an explicit fingerprint to differentiate between the response of polaritons and other untargeted effects.