Understanding the origin of electron-phonon coupling in lead-halide perovskites (LHP) is key to interpreting and leveraging their optical and electronic properties. Here we perform femtosecond-resolved, optical-pump, electron-diffraction-probe measurements to quantify the lattice reorganization occurring as a result of photoexcitation in LHP nanocrystals. Photoexcitation is found to drive a reduction in lead-halide octahedra tilts and distortions in the lattice, a result of deformation potential coupling to low energy optical phonons. Our results indicate particularly strong coupling in FAPbBr3, and far weaker coupling in CsPbBr3, highlighting differences in the dominant machanisms governing electron-phonon coupling in LHPs. We attribute the enhanced coupling in FAPbBr3 to its disordered crystal structure, which persists down to cryogenic temperatures. We find the reorganizations induced by each exciton in a multiexcitonic state constructively interfere, giving rise to a coupling strength which scales quadratically with the exciton number. This superlinear scaling induces phonon-mediated attractive interactions between excitations in LHPs.
@article{arxiv.2203.06286,
title = {Phonon-Mediated Attractive Interactions between Excitons in Lead-Halide-Perovskites},
author = {Nuri Yazdani and Maryna I. Bodnarchuk and Federica Bertolotti and Norberto Masciocchi and Ina Fureraj and Burak Guzelturk and Benjamin L. Cotts and Marc Zajac and Gabriele Rainò and Maximilian Jansen and Simon C. Boehme and Maksym Yarema and Ming-Fu Lin and Michael Kozina and Alexander Reid and Xiaozhe Shen and Stephen Weathersby and Xijie Wang and Eric Vauthey and Antonietta Guagliardi and Maksym V. Kovalenko and Vanessa Wood and Aaron Lindenberg},
journal= {arXiv preprint arXiv:2203.06286},
year = {2022}
}