Superfluorescence from lead halide perovskite quantum dot superlattices

An ensemble of emitters can behave very differently from its individual constituents when they interact coherently via a common light field. After excitation of such an ensemble, collective coupling can give rise to a many-body quantum phenomenon that results in short, intense bursts of light—so-called superfluorescence¹. Because this phenomenon requires a fine balance of interactions between the emitters and their decoupling from the environment, together with close identity of the individual emitters, superfluorescence has thus far been observed only in a limited number of systems, such as certain atomic and molecular gases and a few solid-state systems^2-7. The generation of superfluorescent light in colloidal nanocrystals (which are bright photonic sources practically suited for optoelectronics^8,9) has been precluded by inhomogeneous emission broadening, low oscillator strength, and fast exciton dephasing. Here we show that caesium lead halide (CsPbX₃, X = Cl, Br) perovskite nanocrystals^10-13 that are self-organized into highly ordered three-dimensional superlattices exhibit key signatures of superfluorescence. These are dynamically red-shifted emission with more than 20-fold accelerated radiative decay, extension of the first-order coherence time by more than a factor of four, photon bunching, and delayed emission pulses with Burnham-Chiao ringing behaviour¹⁴ at high excitation density. These mesoscopically extended coherent states could be used to boost the performance of opto-electronic devices¹⁵ and enable entangled multi-photon quantum light sources^16,17.