Unconventional Biexciton Dynamics in Superradiant Perovskite Quantum Dots Driven by Many-Body Correlations

Excitons and biexcitons emission traits, for example, quantum yield, lifetime, and coherence, govern device performance metrics including brightness, optical gain thresholds, and the efficiency of single- and entangled-photon generation. Biexcitons are conventionally understood to radiatively decay more rapidly than excitons. This view stems largely from studies in strongly confined quantum dots (QDs), where inter-exciton correlations are often neglected. In contrast, weakly confined systems such as large CsPbBr₃ QDs exhibit significant Coulomb correlations, necessitating a revised framework for biexciton radiative dynamics, one that has remained incomplete due to limited experimental insights. Here, we combine single-particle photoluminescence (PL) spectroscopy with effective-mass variational quantum Monte Carlo (VQMC) simulations to directly probe the biexciton geometry, exciton-phonon interactions, and radiative decay in CsPbBr₃ QDs across a range of sizes and temperatures. We reveal that the biexciton-to-exciton radiative decay lifetime ratio is strongly modulated by inter-exciton correlations, with a striking inversion of the expected decay lifetime hierarchy in the weak-confinement regime. Specifically, at cryogenic temperatures, biexcitons exhibit anomalously longer radiative lifetime (148 ± 30 ps) than excitons (106 ± 16 ps), challenging conventional models. These findings uncover a correlation-driven regime of multiexciton physics and suggest new routes for tailoring light-matter interactions for classical and quantum photonic applications.