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 systems2,3,4,5,6,7. The generation of superfluorescent light in colloidal nanocrystals (which are bright photonic sources practically suited for optoelectronics8,9) 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 nanocrystals10,11,12,13 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 sources16,17.
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The data that support the findings of this study are available from the corresponding authors upon reasonable request.
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We thank D. J. Norris, C. Schwemmer, D. Urbonas and F. Scafirimuto for helpful discussions. F. Krieg is acknowledged for providing additional samples for control experiments. M.A.B., M.V.K., T.S., R.F.M. and G.R. acknowledge support from the European Union’s Horizon-2020 programme through the Marie-Sklodowska Curie ITN network PHONSI (H2020-MSCA-ITN-642656) and the Swiss State Secretariat for Education Research and Innovation (SERI). M.I.B. acknowledges financial support from the Swiss National Science Foundation (SNF Ambizione grant no. PZENP2_154287). M.V.K. acknowledges financial support from the European Research Council under the European Union’s Seventh Framework Program (FP/2007-2013)/ERC Grant Agreement no. 306733 (NANOSOLID Starting Grant).
Nature thanks C. Kagan and the other anonymous reviewer(s) for their contribution to the peer review of this work.