Long-range transport in excitonic dark states in coupled quantum wells

Abstract

During the past ten years, coupled quantum wells have emerged as a promising system for experiments on Bose condensation of excitons, with numerous theoretical1,2,3,4,5,6 and experimental7,8,9,10,11,12 studies aimed at the demonstration of this effect. One of the issues driving these studies is the possibility of long-range coherent transport of excitons. Excitons in quantum wells typically diffuse only a few micrometres from the spot where they are generated by a laser pulse; their diffusion is limited by their lifetime (typically a few nanoseconds) and by scattering due to disorder in the well structure. Here we report photoluminescence measurements of InGaAs quantum wells and the observation of an effect by which luminescence from excitons appears hundreds of micrometres away from the laser excitation spot. This luminescence appears as a ring around the laser spot; almost none appears in the region between the laser spot and the ring. This implies that the excitons must travel in a dark state until they reach some critical distance, at which they collectively revert to luminescing states. It is unclear whether this effect is related to macroscopic coherence caused by Bose condensation of excitons.

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Figure 1: The band structure of the coupled quantum wells in the presence of electric field.
Figure 2: Spectral images of the luminescence from indirect excitons for various laser powers.
Figure 3: The critical excitation density for appearance of the luminescence ring, as a function of the bath temperature in a variable-temperature cryostat.
Figure 4: Luminescence profile and intensity.

References

  1. 1

    Zhu, X., Littlewood, P. B., Hybertson, M. S. & Rice, T. M. Exciton condensate in semiconductor quantum well structures. Phys. Rev. Lett. 74, 1633–1636 (1995)

    CAS  Article  Google Scholar 

  2. 2

    Fernández-Rossier, J. & Tejedor, C. Spin degree of freedom in two-dimensional condensates. Phys. Rev. Lett. 78, 4809–4812 (1997)

    Article  Google Scholar 

  3. 3

    Lozovik, Yu. E. & Birman, O. L. Phase transitions in a system of spatially separated electrons and holes. JETP Lett. 84, 1027–1035 (1997)

    Article  Google Scholar 

  4. 4

    Yudson, V. I. Charged ‘few-electron–single spatially separated hole’ complexes in a double quantum well near a metal plate. Phys. Rev. B 77, 1564–1567 (1996)

    CAS  Google Scholar 

  5. 5

    Iida, T. & Tsubota, M. Order formation and superfluidity of excitons in type-II semiconductor quantum wells. Phys. Rev. B 60, 5802–5810 (1999)

    CAS  Article  Google Scholar 

  6. 6

    Dzubenko, A. B. & Yablonskii, A. L. Intrawell and interwell magnetoexcitons in InxGa1-x coupled double quantum wells. Phys. Rev. B 53, 16355–16364 (1996)

    Article  Google Scholar 

  7. 7

    Larionov, A. V. & Timofeev, V. B. Condensation of interwell excitons in GaAs/AlGaAs double quantum wells. JETP Lett. 73, 342–350 (2001)

    Article  Google Scholar 

  8. 8

    Krivolapchuk, V. V., Moskalenko, E. S., Zhmodikov, A. L., Cheng, T. S. & Foxon, C. T. Collective properties of spatially indirect excitons in asymmetric GaAs/AlGaAs double quantum wells. Solid State Commun. 111, 49–54 (1999)

    CAS  Article  Google Scholar 

  9. 9

    Butov, L. V. & Finin, A. I. Anomalous transport and luminesence of indirect excitons in AlAs/GaAs coupled quantum wells as evidence for exciton condensation. Phys. Rev. B 58, 1980–2000 (1998)

    CAS  Article  Google Scholar 

  10. 10

    Butov, L. V., Lai, C. W., Ivanov, A. L., Gossard, A. C. & Chemla, D. S. Towards Bose–Einstein condensation of excitons in potential traps. Nature 417, 47–52 (2002)

    CAS  Article  Google Scholar 

  11. 11

    Negoita, V., Snoke, D. W. & Eberl, K. Stretching quantum wells: a method for trapping free carriers in GaAs heterostructures. Appl. Phys. Lett. 75, 2059–2061 (1999)

    CAS  Article  Google Scholar 

  12. 12

    Negoita, V., Hackworth, D., Snoke, D. W. & Eberl, K. Sub-Hz spectral fluctuations from high-density excitons in biased coupled quantum wells. Opt. Lett. 25, 572–574 (2000)

    CAS  Article  Google Scholar 

  13. 13

    Negoita, V., Snoke, D. W. & Eberl, K. Harmonic potential traps for indirect excitons in coupled quantum wells. Phys. Rev. B 60, 2661–2669 (1999)

    CAS  Article  Google Scholar 

  14. 14

    Fox, A. M., Miller, D. A. B., Livescu, G., Cunningham, J. E. & Yan, W. Y. Excitonic effects in coupled quantum wells. Phys. Rev. B 44, 6231–6242 (1991)

    CAS  Article  Google Scholar 

  15. 15

    Kato, Y., Takahashi, Y., Fukatsu, S., Shiraki, Y. & Ito, R. Observation of the Stark effect in coupled quantum wells by electroluminescence and circularly polarized photoluminescence excitation spectroscopy. J. Appl. Phys. 75, 7476–7481 (1994)

    CAS  Article  Google Scholar 

  16. 16

    Negoita, V., Snoke, D. W. & Eberl, K. Huge density-dependent blueshift of indirect excitons in biased coupled quantum wells. Phys. Rev. B 61, 2779–2783 (2000)

    CAS  Article  Google Scholar 

  17. 17

    Moskalenko, S. A. & Snoke, D. W. Bose-Einstein Condensation of Excitons and Biexcitons (Cambridge Univ. Press, Cambridge, 2000)

    Google Scholar 

  18. 18

    Bagaev, V. S., Keldysh, L. V., Sibeldin, N. N. & Tsvetkov, V. A. Phonon wind drag of excitons and electron-hole drops. Sov. Phys. JETP 70, 702–716 (1976)

    CAS  Google Scholar 

  19. 19

    Hensel, J. C. & Dynes, R. C. Interaction of electron-hole drops with ballistic phonons in heat pulses: The phonon wind. Phys. Rev. Lett. 39, 969–972 (1977)

    CAS  Article  Google Scholar 

  20. 20

    Greenstein, M. & Wolfe, J. P. Anisotropy in the shape of the electron-hole-droplet cloud in germanium. Phys. Rev. Lett. 41, 715–719 (1978)

    CAS  Article  Google Scholar 

  21. 21

    Snoke, D. W., Rühle, W. W., Köhler, K. & Ploog, K. Spin flip of excitons in GaAs quantum wells. Phys. Rev. B 55, 13789–13794 (1997)

    CAS  Article  Google Scholar 

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Acknowledgements

This work has been supported by the National Science Foundation and by the Department of Energy. We thank V. Negoita for early contributions to these experiments.

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Correspondence to D. Snoke.

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The authors declare that they have no competing financial interests.

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Snoke, D., Denev, S., Liu, Y. et al. Long-range transport in excitonic dark states in coupled quantum wells. Nature 418, 754–757 (2002). https://doi.org/10.1038/nature00940

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