Quantum Exciton Transport in Perovskite Nanocrystal Superlattices

At the most fundamental level, transport of energy carriers in solid-state materials is determined by their wavefunctions and their interactions with the environment. While quantum transport theory has predicted distinct transport regimes resulting from the intricate interplay between coherent wave-like and incoherent particle-like mechanisms, these predictions are awaiting experimental verification. This study demonstrates unambiguous signatures of quantum transport in perovskite nanocrystal (NC) superlattices by directly imaging exciton propagation with high spatial and temporal resolutions over 7-298 K. At 7 K, coherent propagation of the excitons dominates, with transient ballistic motion within a coherence length that extends up to 40 NC sites. The interference of the wave-like motion leads to Anderson Localization in the long-time limit. As temperature increases, a peak in the long-time diffusion constant is observed at a temperature where static disorder and dephasing are balanced, which substantiates direct evidence for environment-assisted quantum transport (ENAQT). We established a strong correlation between theoretical predictions and experimental measurements using a stochastic Anderson localization model. These results provide a fundamental understanding of quantum transport that interpolated coherent and incoherent limits in disordered systems and highlight perovskite NCs as promising building blocks for quantum materials.