Giant Rydberg excitons in the copper oxide Cu2O

Abstract

A highly excited atom having an electron that has moved into a level with large principal quantum number is a hydrogen-like object, termed a Rydberg atom. The giant size of Rydberg atoms1 leads to huge interaction effects. Monitoring these interactions has provided insights into atomic and molecular physics on the single-quantum level. Excitons—the fundamental optical excitations in semiconductors2, consisting of an electron and a positively charged hole—are the condensed-matter analogues of hydrogen. Highly excited excitons with extensions similar to those of Rydberg atoms are of interest because they can be placed and moved in a crystal with high precision using microscopic energy potential landscapes. The interaction of such Rydberg excitons may allow the formation of ordered exciton phases or the sensing of elementary excitations in their surroundings on a quantum level. Here we demonstrate the existence of Rydberg excitons in the copper oxide Cu2O, with principal quantum numbers as large as n = 25. These states have giant wavefunction extensions (that is, the average distance between the electron and the hole) of more than two micrometres, compared to about a nanometre for the ground state. The strong dipole–dipole interaction between such excitons is indicated by a blockade effect in which the presence of one exciton prevents the excitation of another in its vicinity.

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Figure 1: High-resolution absorption spectra of yellow P excitons in Cu2O.
Figure 2: Dependences of experimentally determined parameters of P-exciton lines on principal quantum number n, revealing power-law behaviour.
Figure 3: Reduction of excitonic absorption due to dipole blockade.

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Acknowledgements

We thank R. Hönig for experimental support with the first measurements. We acknowledge financial support by the Deutsche Forschungsgemeinschaft (BA 1549/18-1 and SFB 652 Strong correlations and collective effects in radiation fields). M.B. acknowledges support from the Russian Ministry of Science and Education (contract number 14.Z50.31.0021).

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T.K., D.F. and M.B. conceived, designed and carried out the experiments. H.S. and S.S. contributed through the Rydberg blockade model. All authors cooperated in data analysis, discussions and preparation of the manuscript.

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Correspondence to D. Fröhlich.

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The authors declare no competing financial interests.

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This file contains Supplementary Text, Supplementary Figures 1-5, Supplementary Table 1 and Supplementary References. (PDF 452 kb)

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Kazimierczuk, T., Fröhlich, D., Scheel, S. et al. Giant Rydberg excitons in the copper oxide Cu2O. Nature 514, 343–347 (2014). https://doi.org/10.1038/nature13832

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