Recent experimental and computational studies suggest that biexcitons (BX) confined in large CsPbBr3 nanocrystals experience reduced dielectric screening as compared to excitons (X) and trions (X∗). Here we provide a physical rationale to explain such a behavior. A characteristic frequency is introduced, which describes the internal dynamics of an exciton within the excitonic complex. By means of effective mass--variational Quantum Monte Carlo simulations, we show that, in large nanocrystals, the frequency is similar for X and X∗, but smaller for BX. Because the frequencies exceed that of the bulk longitudinal optical phonon, this leads to a reduced dielectric constant for BX, which is in contrast with the behavior of strongly confined nanocrystals.
@article{arxiv.2507.11087,
title = {Internal dynamics and dielectric screening of confined multiexciton states},
author = {Josep Planelles and Juan I. Climente and Jose L. Movilla},
journal= {arXiv preprint arXiv:2507.11087},
year = {2025}
}