Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)
DOI: https://doi.org/10.29363/nanoge.matsusfall.2024.223
Publication date: 28th August 2024
Absorption of light via interband optical transitions constitutes a primary process in nature, e.g., in photosynthesis, as well as in applied technologies, e.g., in solar photovoltaic cells, photodetectors, or (quantum) light-matter interfaces. In cavity-free systems, engineerability of the rate of absorption has thus far been limited, consistent with the wide-spread belief that the coupling strength between initial and final state (described by the square of the matrix element of the light-matter interaction in Fermi’s golden rule) is an intrinsic parameter of the employed material. However, enhanced absorption rates could be realized via giant-oscillator-strength (GOS) transitions, leveraging coherent oscillations of the electron polarization in a volume significantly larger than a unit cell.[1] While experimental evidence for such a superradiance phenomenon has indeed already been provided in emission processes, realizations in an absorption process, i.e., in the form of “superabsorption”, have been sparse and/or require complicated excited-state engineering approaches.[2]
Here, employing colloidal CsPbBr3 perovskite QDs, we demonstrate a robust and straightforward implementation of superabsorption as a time-reversal process of single-photon superradiance.[3][4] Optical spectroscopy reveals that the band-edge absorption in large CsPbBr3 perovskite QDs exhibits a superlinear increase with QD volume, consistent with the 3D delocalization of a giant exciton wavefunction. Calculations based on the configuration-interaction framework attribute this behavior to strong electronic correlations, and fully corroborate the experimental findings. Our results shed light on a process as fundamental as light absorption, in a new class of commercially relevant direct semiconductors, and may facilitate the development of more efficient optoelectronic devices and new quantum light-matter interfaces.
The project was supported by the European Union's Horizon 2020 program, through a FET Open research and innovation action under Grant Agreement No. 899141 (PoLLoC). This work was also supported by the Weizmann-ETH Zurich Bridge Program, by the Air Force Office of Scientific Research under award number FA8655-21-1 7013 and by the Swiss National Science Foundation (Grant No. 200021_192308, "Q-Light-Engineered Quantum Light Sources with Nanocrystal Assemblies").
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