Exciton polariton condensation in a perovskite moiré flat band at room temperature.

Moiré superlattices exhibit fascinating moiré flat bands when two layers of van der Waals materials are twisted at specific magic angles, providing unparalleled opportunities to explore unconventional correlated quantum phenomena. Exciton polaritons, hybrid quasiparticles of excitons and photons, have emerged as promising synthetic platforms for exploring moiré physics beyond conventional systems. However, the realization of moiré exciton-polariton flat bands and their condensation remains challenging. Here, we experimentally demonstrate a moiré exciton-polariton flat band with condensation in a perovskite moiré superlattice at room temperature. By engineering a 21.79° magic-angle moiré superlattice potential with enhanced interlayer coupling, we experimentally observe a polaritonic moiré flat band near the corresponding monolayer's Dirac points position in the perovskite microcavity. Under a nonresonant pulsed excitation, polaritons with proper detuning condense into the moiré flat band at room temperature. Our work provides a unique platform for investigating exotic moiré phenomena and unlocks promising avenues toward advanced polaritonic devices.