Letter | Published:

Observation of biexcitons in monolayer WSe2

Nature Physics volume 11, pages 477481 (2015) | Download Citation

Abstract

Transition metal dichalcogenide (TMDC) crystals exhibit new emergent properties at monolayer thickness1,2, notably strong many-body effects mediated by Coulomb interactions3,4,5,6. A manifestation of these many-body interactions is the formation of excitons, bound electron–hole pairs, but higher-order excitonic states are also possible. Here we demonstrate the existence of four-body, biexciton states in monolayer WSe2. The biexciton is identified as a sharply defined state in photoluminescence at high exciton density. Its binding energy of 52 meV is more than an order of magnitude greater than that found in conventional quantum-well structures7. A variational calculation of the biexciton state reveals that the high binding energy arises not only from strong carrier confinement, but also from reduced and non-local dielectric screening. These results open the way for the creation of new correlated excitonic states linking the degenerate valleys in TMDC crystals, as well as more complex many-body states such as exciton condensates or the recently reported dropletons8.

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References

  1. 1.

    , , , & Atomically thin MoS: A new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).

  2. 2.

    et al. Emerging photoluminescence in monolayer MoS2. Nano Lett. 10, 1271–1275 (2010).

  3. 3.

    et al. Exciton binding energy and nonhydrogenic Rydberg series in monolayer WS2. Phys. Rev. Lett. 113, 076802 (2014).

  4. 4.

    et al. Probing excitonic dark states in single-layer tungsten disulphide. Nature 513, 214–218 (2014).

  5. 5.

    et al. Tightly bound excitons in monolayer WSe2. Phys. Rev. Lett. 113, 026803 (2014).

  6. 6.

    et al. Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor. Nature Mater. 13, 1091–1095 (2014).

  7. 7.

    Semiconductor Optics Vol. 3 (Springer, 2007).

  8. 8.

    et al. Quantum droplets of electrons and holes. Nature 506, 471–475 (2014).

  9. 9.

    , , & Control of valley polarization in monolayer MoS2 by optical helicity. Nature Nanotech. 7, 494–498 (2012).

  10. 10.

    , , , & Valley polarization in MoS2 monolayers by optical pumping. Nature Nanotech. 7, 490–493 (2012).

  11. 11.

    et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nature Commun. 3, 887 (2012).

  12. 12.

    et al. Optical generation of excitonic valley coherence in monolayer WSe2. Nature Nanotech. 8, 634–638 (2013).

  13. 13.

    , , & Valleytronics. The valley Hall effect in MoS(2) transistors. Science 344, 1489–1492 (2014).

  14. 14.

    et al. Tightly bound trions in monolayer MoS2. Nature Mater. 12, 207–211 (2013).

  15. 15.

    et al. Electrical control of neutral and charged excitons in a monolayer semiconductor. Nature Commun. 4, 1474 (2013).

  16. 16.

    et al. Optical manipulation of the exciton charge state in single-layer tungsten disulfide. Phys. Rev. B 88, 245403 (2013).

  17. 17.

    , & Thermodynamics of biexcitons in a GaAs quantum well. Phys. Rev. B 50, 15099–15107 (1994).

  18. 18.

    , , & Biexciton creation and recombination in a GaAs quantum well. Phys. Rev. B 45, 4308–4311 (1992).

  19. 19.

    et al. Detection of a biexciton in semiconducting carbon nanotubes using nonlinear optical spectroscopy. Phys. Rev. Lett. 109, 197402 (2012).

  20. 20.

    et al. Biexciton, single carrier, and trion generation dynamics in single-walled carbon nanotubes. Phys. Rev. B 87, 205412 (2013).

  21. 21.

    Semiconductor and Metal Nanocrystals: Synthesis and Electronic and Optical Properties (CRC Press, 2003).

  22. 22.

    et al. Many-body effects in valleytronics: Direct measurement of valley lifetimes in single-layer MoS2. Nano Lett. 14, 202–206 (2014).

  23. 23.

    et al. Observation of excitonic fine structure in a 2D transition-metal dichalcogenide semiconductor. ACS Nano 9, 647–655 (2015).

  24. 24.

    et al. Defects activated photoluminescence in two-dimensional semiconductors: Interplay between bound, charged, and free excitons. Sci. Rep. 3, 02657 (2013).

  25. 25.

    et al. Valley dynamics probed through charged and neutral exciton emission in monolayer WSe2. Phys. Rev. B 90, 075413 (2014).

  26. 26.

    , , , & Binding of quasi-two-dimensional biexcitons. Phys. Rev. Lett. 76, 672–675 (1996).

  27. 27.

    et al. Polarization-dependent formation of biexcitons in (Zn, Cd)Se/ZnSe quantum wells. Phys. Rev. B 55, 9866–9871 (1997).

  28. 28.

    et al. Exciton–exciton annihilation in MoSe2 monolayers. Phys. Rev. B 89, 125427 (2014).

  29. 29.

    et al. Observation of rapid exciton–exciton annihilation in monolayer molybdenum disulfide. Nano Lett. 14, 5625–5629 (2014).

  30. 30.

    , & Theory of neutral and charged excitons in monolayer transition metal dichalcogenides. Phys. Rev. B 88, 045318 (2013).

  31. 31.

    , , , & Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides. Phys. Rev. B 88, 085433 (2013).

  32. 32.

    Binding energy of biexcitons and bound excitons in quantum wells. Phys. Rev. B 28, 871–879 (1983).

  33. 33.

    , , & Binding energy of two-dimensional biexcitons. Phys. Rev. B 53, 15909–15913 (1996).

  34. 34.

    , & Excitons and charged excitons in semiconductor quantum wells. Phys. Rev. B 61, 13873–13881 (2000).

  35. 35.

    , & Dielectric screening in two-dimensional insulators: Implications for excitonic and impurity states in graphane. Phys. Rev. B 84, 085406 (2011).

  36. 36.

    , & Stability of two- and three-dimensional excitonic complexes. Phys. Rev. B 59, 5652–5661 (1999).

  37. 37.

    , , , & Ultrafast biexciton spectroscopy in semiconductor quantum dots: Evidence for early emergence of multiple-exciton generation. Sci. Rep. 3, 3206 (2013).

  38. 38.

    et al. Entangled photon pairs from semiconductor quantum dots. Phys. Rev. Lett. 96, 130501 (2006).

  39. 39.

    et al. Measurement of the optical dielectric function of monolayer transition-metal dichalcogenides: MoS2, MoSe2, WS2, and WSe2. Phys. Rev. B 90, 205422 (2014).

  40. 40.

    et al. Photocarrier relaxation pathway in two-dimensional semiconducting transition metal dichalcogenides. Nature Commun. 5, 4543 (2014).

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Acknowledgements

The authors would like to acknowledge valuable discussions with A. Chernikov and T. Cao and technical assistance from Y. Rao and F. Zhang. The experimental research was supported by the National Science Foundation through grants DMR-1106172 and DMR-1122594, the Keck Foundation, and the Honda Research Institute. Support for data analysis by was provided by the AMOS program, Chemical Sciences, Geosciences, and Biosciences Division, Basic Energy Sciences, US Department of Energy under Contract No. DE-AC02-76-SFO0515 (T.F.H.). This work was carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the US Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886 (M.S.H.).

Author information

Author notes

    • Yumeng You
    •  & Xiao-Xiao Zhang

    These authors contributed equally to this work.

    • Tony F. Heinz

    Present addresses: Department of Applied Physics, Stanford University, Stanford, California 94305, USA; SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA.

Affiliations

  1. Ordered Matter Science Research Center, Southeast University, Nanjing 211189, China

    • Yumeng You
  2. Departments of Physics and Electrical Engineering, Columbia University, 538 West 120th St., New York, New York 10027, USA

    • Yumeng You
    • , Xiao-Xiao Zhang
    •  & Tony F. Heinz
  3. Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA

    • Timothy C. Berkelbach
    •  & David R. Reichman
  4. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973-5000, USA

    • Mark S. Hybertsen

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Contributions

Y.Y. and X-X.Z. designed the experiment, performed the measurements, interpreted the results, and wrote the manuscript; T.C.B. performed the variational calculation under the guidance of M.S.H. and D.R.R. and contributed to writing of the manuscript; T.F.H. contributed to the interpretation of the results and writing of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Tony F. Heinz.

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https://doi.org/10.1038/nphys3324

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