Abstract

The long-lived interlayer excitons in van der Waals heterostructures based on transition-metal dichalcogenides, together with unique spin–valley physics, make them promising for next-generation photonic and valleytronic devices. Although the emission characteristics of interlayer excitons have been studied, efficient manipulation of their valley states, a necessary requirement for information encoding, is still lacking. Here, we demonstrate comprehensive electrical control of interlayer excitons in a MoSe2/WSe2 heterostructure. Encapsulation of our well-aligned stack with hexagonal boron nitride (h-BN) allows us to resolve two separate narrow interlayer transitions with opposite helicities under circularly polarized excitation, either preserving or reversing the polarization of incoming light. By electrically controlling their relative intensities, we realize a polarization switch with tunable emission intensity and wavelength. Finally, we observe large g-factors of these two transitions on application of an external magnetic field. These results are interpreted within the picture of moiré-induced brightening of forbidden optical transitions. The ability to control the polarization of interlayer excitons is a step towards the manipulation of the valley degree of freedom in realistic device applications.

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The data that support the findings of this study are available from the corresponding author on reasonable request.

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References

  1. 1.

    Žutić, I., Fabian, J. & Das Sarma, S. Spintronics: fundamentals and applications. Rev. Mod. Phys. 76, 323–410 (2004).

  2. 2.

    Rycerz, A., Tworzydło, J. & Beenakker, C. W. J. Valley filter and valley valve in graphene. Nat. Phys. 3, 172–175 (2007).

  3. 3.

    Gunawan, O. et al. Valley susceptibility of an interacting two-dimensional electron system. Phys. Rev. Lett. 97, 186404 (2006).

  4. 4.

    Radisavljevic, B., Radenovic, A., Brivio, J., Giacometti, V. & Kis, A. Single-layer MoS2 transistors. Nat. Nanotech. 6, 147–150 (2011).

  5. 5.

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

  6. 6.

    Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nat. Nanotech. 7, 494–498 (2012).

  7. 7.

    Wang, Q. H., Kalantar-Zadeh, K., Kis, A., Coleman, J. N. & Strano, M. S. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nat. Nanotech. 7, 699–712 (2012).

  8. 8.

    Manzeli, S., Ovchinnikov, D., Pasquier, D., Yazyev, O. V. & Kis, A. 2D transition metal dichalcogenides. Nat. Rev. Mater. 2, 1733 (2017).

  9. 9.

    Xiao, D., Liu, G.-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).

  10. 10.

    Xu, X., Yao, W., Xiao, D. & Heinz, T. F. Spin and pseudospins in layered transition metal dichalcogenides. Nat. Phys. 10, 343–350 (2014).

  11. 11.

    Schaibley, J. R. et al. Valleytronics in 2D materials. Nat. Rev. Mater. 1, 16055 (2016).

  12. 12.

    Unuchek, D. et al. Room-temperature electrical control of exciton flux in a van der Waals heterostructure. Nature 560, 340–344 (2018).

  13. 13.

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

  14. 14.

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

  15. 15.

    Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nat. Nanotech. 7, 490–493 (2012).

  16. 16.

    Fang, H. et al. Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides. Proc. Natl Acad. Sci. USA 111, 6198–6202 (2014).

  17. 17.

    Rivera, P. et al. Observation of long-lived interlayer excitons in monolayer MoSe2–WSe2 heterostructures. Nat. Commun. 6, 6242 (2015).

  18. 18.

    Hsu, W.-T. et al. Negative circular polarization emissions from WSe2 /MoSe2 commensurate heterobilayers. Nat. Commun. 9, 1356 (2018).

  19. 19.

    Rivera, P. et al. Valley-polarized exciton dynamics in a 2D semiconductor heterostructure. Science 351, 688–691 (2016).

  20. 20.

    Hunt, B. et al. Massive Dirac fermions and Hofstadter butterfly in a van der Waals heterostructure. Science 340, 1427–1430 (2013).

  21. 21.

    Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).

  22. 22.

    Yu, H., Liu, G.-B., Tang, J., Xu, X. & Yao, W. Moiré excitons: from programmable quantum emitter arrays to spin-orbit–coupled artificial lattices. Sci. Adv. 3, e1701696 (2017).

  23. 23.

    Yu, H., Liu, G.-B. & Yao, W. Brightened spin-triplet interlayer excitons and optical selection rules in van der Waals heterobilayers. 2D Mater. 5, 035021 (2018).

  24. 24.

    Mayorov, A. S. et al. Micrometer-scale ballistic transport in encapsulated graphene at room temperature. Nano Lett. 11, 2396–2399 (2011).

  25. 25.

    Dean, C. R. et al. Boron nitride substrates for high-quality graphene electronics. Nat. Nanotech. 5, 722–726 (2010).

  26. 26.

    Kormányos, A., Zólyomi, V., Drummond, N. D. & Burkard, G. Spin-orbit coupling, quantum dots, and qubits in monolayer transition metal dichalcogenides. Phys. Rev. X 4, 011034 (2014).

  27. 27.

    Hanbicki, A. T. et al. Double indirect interlayer exciton in a MoSe2/WSe2 van der Waals heterostructure. ACS Nano 12, 4719–4726 (2018).

  28. 28.

    Koma, A. Van der Waals epitaxy for highly lattice-mismatched systems. J. Cryst. Growth 201, 236–241 (1999).

  29. 29.

    Kang, J., Tongay, S., Zhou, J., Li, J. & Wu, J. Band offsets and heterostructures of two-dimensional semiconductors. Appl. Phys. Lett. 102, 012111 (2013).

  30. 30.

    He, J., Hummer, K. & Franchini, C. Stacking effects on the electronic and optical properties of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. Phys. Rev. B 89, 075409 (2014).

  31. 31.

    Wang, G. et al. Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers. Appl. Phys. Lett. 106, 112101 (2015).

  32. 32.

    Aivazian, G. et al. Magnetic control of valley pseudospin in monolayer WSe2. Nat. Phys. 11, 148–152 (2015).

  33. 33.

    Srivastava, A. et al. Valley Zeeman effect in elementary optical excitations of monolayer WSe2. Nat. Phys. 11, 141–147 (2015).

  34. 34.

    Nagler, P. et al. Giant magnetic splitting inducing near-unity valley polarization in van der Waals heterostructures. Nat. Commun. 8, 1551 (2017).

  35. 35.

    Wu, F., Lovorn, T. & MacDonald, A. H. Theory of optical absorption by interlayer excitons in transition metal dichalcogenide heterobilayers. Phys. Rev. B 97, 035306 (2018).

  36. 36.

    Miller, B. et al. Long-lived direct and indirect interlayer excitons in van der Waals heterostructures. Nano Lett. 17, 5229–5237 (2017).

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Acknowledgements

We acknowledge W. Yao, A. Chernikov and B. Urbaszek for discussions. We thank Z. Benes of CMi for help with electron beam lithography. D.U., A.C., A.A. and A.K. acknowledge support by the Swiss National Science Foundation (grant 153298), H2020 European Research Council (ERC, grant 682332), and Marie Curie-Sklodowska-Curie Actions (COFUND grant 665667). A.K. acknowledges funding from the European Union’s Horizon H2020 Future and Emerging Technologies under grant agreements 696656 and 785219 (Graphene Flagship). K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan, and from JSPS KAKENHI grant numbers JP15K21722 and JP25106006.

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Author notes

  1. These authors contributed equally: Alberto Ciarrocchi, Dmitrii Unuchek.

Affiliations

  1. Electrical Engineering Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

    • Alberto Ciarrocchi
    • , Dmitrii Unuchek
    • , Ahmet Avsar
    •  & Andras Kis
  2. Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

    • Alberto Ciarrocchi
    • , Dmitrii Unuchek
    • , Ahmet Avsar
    •  & Andras Kis
  3. National Institute for Materials Science, 1–1 Namiki, Tsukuba, Japan

    • Kenji Watanabe
    •  & Takashi Taniguchi

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Contributions

A.K. initiated and supervised the project. A.C. fabricated the devices. K.W. and T.T. grew the h-BN crystals. D.U. performed the optical measurements, assisted by A.C. A.C. and D.U. analysed the data with input from A.A. and A.K. All authors contributed to the writing of the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Andras Kis.

Supplementary information

  1. Supplementary Information

    This file contains more information about the work and Supplementary Figures 1–13.

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DOI

https://doi.org/10.1038/s41566-018-0325-y