Abstract
In neutral dense electronâhole systems at low temperatures, theory predicted Cooper-pair-like excitons exist at the Fermi energy and form a BardeenâCooperâSchrieffer-like condensate. Optical excitations create electronâhole systems with the density controlled via the excitation power. However, the intense optical excitations required to achieve high densities cause substantial heating that prevents the realization of simultaneously dense and cold electronâhole systems in conventional semiconductors. Here we show that the separation of electron and hole layers enables the realization of a simultaneously dense and cold electronâhole system. We find a strong enhancement of photoluminescence intensity at the Fermi energy of the neutral dense ultracold electronâhole system that demonstrates the emergence of an excitonic Fermi edge singularity due to the formation of Cooper-pair-like excitons at the Fermi energy. Our measurements also show a crossover from the hydrogen-like excitons to the Cooper-pair-like excitons with increasing density, consistent with the theoretical prediction of a smooth transition.
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Source data files are available via Figshare66. All relevant data are available from the authors upon reasonable request.
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Acknowledgements
We thank M. Fogler, L. Fowler-Gerace, J. Leonard, L. Sham and B. Vermilyea for discussions. The spectroscopy studies were supported by NSF grant no. 1905478 (L.V.B.). The coherence studies were supported by DOE Office of Basic Energy Sciences under award no. DE-FG02-07ER46449 (L.V.B.). The heterostructure growth was funded by the Gordon and Betty Moore Foundationâs EPiQS Initiative, grant GBMF9615 to L.N.P., and by National Science Foundation MRSEC grant DMR 2011750 to Princeton University.
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L.V.B. designed the project. K.W.B. and L.N.P. grew the GaAs heterostructures. D.J.C. and E.A.S. performed the measurements. D.J.C., E.A.S. and L.V.B. analysed the data. L.V.B. wrote the manuscript with inputs from all the authors.
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Choksy, D.J., Szwed, E.A., Butov, L.V. et al. Fermi edge singularity in neutral electronâhole system. Nat. Phys. 19, 1275â1279 (2023). https://doi.org/10.1038/s41567-023-02096-2
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DOI: https://doi.org/10.1038/s41567-023-02096-2