Ultrafast transition between exciton phases in van der Waals heterostructures

Abstract

Heterostructures of atomically thin van der Waals bonded monolayers have opened a unique platform to engineer Coulomb correlations, shaping excitonic1,2,3, Mott insulating4 or superconducting phases5,6. In transition metal dichalcogenide heterostructures7, electrons and holes residing in different monolayers can bind into spatially indirect excitons1,3,8,9,10,11 with a strong potential for optoelectronics11,12, valleytronics1,3,13, Bose condensation14, superfluidity14,15 and moiré-induced nanodot lattices16. Yet these ideas require a microscopic understanding of the formation, dissociation and thermalization dynamics of correlations including ultrafast phase transitions. Here we introduce a direct ultrafast access to Coulomb correlations between monolayers, where phase-locked mid-infrared pulses allow us to measure the binding energy of interlayer excitons in WSe2/WS2 hetero-bilayers by revealing a novel 1s–2p resonance, explained by a fully quantum mechanical model. Furthermore, we trace, with subcycle time resolution, the transformation of an exciton gas photogenerated in the WSe2 layer directly into interlayer excitons. Depending on the stacking angle, intra- and interlayer species coexist on picosecond scales and the 1s–2p resonance becomes renormalized. Our work provides a direct measurement of the binding energy of interlayer excitons and opens the possibility to trace and control correlations in novel artificial materials.

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Fig. 1: NIR pump–MIR probe spectroscopy of a WSe2/WS2 hetero-bilayer.
Fig. 2: Dielectric response of intra- and interlayer excitons and excitonic wavefunctions.
Fig. 3: Temporal evolution of the dielectric response in experiment and theory.
Fig. 4: Ultrafast evolution of intra- and interlayer exciton densities and microscopic model.

Data availability

The data sets generated during and/or analysed during the current study are available from the corresponding author upon reasonable request.

References

  1. 1.

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

    CAS  Article  Google Scholar 

  2. 2.

    Ju, L. et al. Tunable excitons in bilayer graphene. Science 358, 907–910 (2017).

    CAS  Article  Google Scholar 

  3. 3.

    Jin, C. et al. Imaging of pure spin-valley diffusion current in WS2–WSe2 heterostructures. Science 360, 893–896 (2018).

    CAS  Article  Google Scholar 

  4. 4.

    Cao, Y. et al. Correlated insulator behaviour at half-filling in magic-angle graphene superlattices. Nature 556, 80–84 (2018).

    CAS  Article  Google Scholar 

  5. 5.

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

    CAS  Article  Google Scholar 

  6. 6.

    Lee, J. J. et al. Interfacial mode coupling as the origin of the enhancement of T c in FeSe films on SrTiO3. Nature 515, 245–248 (2014).

    CAS  Article  Google Scholar 

  7. 7.

    Gong, Y. et al. Vertical and in-plane heterostructures from WS2/MoS2 monolayers. Nat. Mater. 13, 1135–1142 (2014).

    CAS  Article  Google Scholar 

  8. 8.

    Hong, X. et al. Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures. Nat. Nanotechnol. 9, 682–686 (2014).

    CAS  Article  Google Scholar 

  9. 9.

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

    CAS  Article  Google Scholar 

  10. 10.

    Arora, A. et al. Interlayer excitons in a bulk van der Waals semiconductor. Nat. Commun. 8, 639 (2017).

    Article  Google Scholar 

  11. 11.

    Ross, J. S. et al. Interlayer exciton optoelectronics in a 2D heterostructure p–n junction. Nano Lett. 17, 638–643 (2017).

    CAS  Article  Google Scholar 

  12. 12.

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

    CAS  Article  Google Scholar 

  13. 13.

    Baranowski, M. et al. Probing the interlayer exciton physics in a MoS2/MoSe2/MoS2 van der Waals heterostructure. Nano Lett. 17, 6360–6366 (2017).

    CAS  Article  Google Scholar 

  14. 14.

    Su, J.-J. & MacDonald, A. H. How to make a bilayer exciton condensate flow. Nat. Phys. 4, 799–802 (2008).

    CAS  Article  Google Scholar 

  15. 15.

    Fogler, M. M., Butov, L. V. & Novoselov, K. S. High-temperature superfluidity with indirect excitons in van der Waals heterostructures. Nat. Commun. 5, 4555 (2014).

    CAS  Article  Google Scholar 

  16. 16.

    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).

    Article  Google Scholar 

  17. 17.

    Ugeda, M. M. et al. Giant band gap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor. Nat. Mater. 13, 1091–1095 (2014).

    CAS  Article  Google Scholar 

  18. 18.

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

    Article  Google Scholar 

  19. 19.

    Poellmann, C. et al. Resonant internal quantum transitions and femtosecond radiative decay of excitons in monolayer WSe2. Nat. Mater. 14, 889–893 (2015).

    CAS  Article  Google Scholar 

  20. 20.

    Steinleitner, P. et al. Dielectric engineering of electronic correlations in a van der Waals heterostructure. Nano Lett. 18, 1402–1409 (2018).

    CAS  Article  Google Scholar 

  21. 21.

    Chen, H. et al. Ultrafast formation of interlayer hot excitons in atomically thin MoS2/WS2 heterostructures. Nat. Commun. 7, 12512 (2016).

    CAS  Article  Google Scholar 

  22. 22.

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

    CAS  Article  Google Scholar 

  23. 23.

    Kunstmann, J. et al. Momentum-space indirect interlayer excitons in transition-metal dichalcogenide van der Waals heterostructures. Nat. Phys. 14, 801–805 (2018).

    CAS  Article  Google Scholar 

  24. 24.

    Mounet, N. et al. Two-dimensional materials from high-throughput computational exfoliation of experimentally known compounds. Nat. Nanotechnol. 13, 246–252 (2018).

    CAS  Article  Google Scholar 

  25. 25.

    Huber, R. et al. How many-particle interactions develop after ultrafast excitation of an electron-hole plasma. Nature 414, 286–289 (2001).

    CAS  Article  Google Scholar 

  26. 26.

    Kaindl, R. A., Carnahan, M. A., Hägele, D., Lövenich, R. & Chemla, D. S. Ultrafast terahertz probes of transient conducting and insulating phases in an electron–hole gas. Nature 423, 734–738 (2003).

    CAS  Article  Google Scholar 

  27. 27.

    Luo, L. et al. Ultrafast terahertz snapshots of excitonic Rydberg states and electronic coherence in an organometal halide perovskite. Nat. Commun. 8, 15565 (2017).

    CAS  Article  Google Scholar 

  28. 28.

    Ulbricht, R., Hendry, E., Shan, J., Heinz, T. F. & Bonn, M. Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy. Rev. Mod. Phys. 83, 543 (2011).

    CAS  Article  Google Scholar 

  29. 29.

    Wang, K. et al. Interlayer coupling in twisted WSe2/WS2 bilayer heterostructures revealed by optical spectroscopy. ACS Nano 10, 6612–6622 (2016).

    CAS  Article  Google Scholar 

  30. 30.

    Brem, S., Selig, M., Berghaeuser, G. & Malic, E. Exciton relaxation cascade in two-dimensional transition metal dichalcogenides. Sci. Rep. 8, 8238 (2018).

    Article  Google Scholar 

  31. 31.

    Castellanos-Gomez, A. et al. Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping. 2D Mater. 1, 011002 (2014).

    Article  Google Scholar 

  32. 32.

    Leandro, M. et al. Observation of intense second harmonic generation from MoS2 atomic crystals. Phys. Rev. B 87, 201401 (2014).

    Google Scholar 

  33. 33.

    Berghäuser, G. et al. Mapping of the dark exciton landscape in transition metal dichalcogenides. Phys. Rev. B 98, 020301 (2018).

    Article  Google Scholar 

  34. 34.

    Laturia, A., Van de Put, M. & Vandenberghe, W. Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk. NPJ 2D Mater. Appl. 2, 6 (2018).

    Article  Google Scholar 

  35. 35.

    Berkelbach, T., Hybertsen, M. & Reichman, D. Theory of neutral and charged excitons in monolayer transition dichalcogenides. Phys. Rev. B 88, 045318 (2013).

    Article  Google Scholar 

  36. 36.

    Kormányos, A. et al. k·p theory for two-dimensional transition metal dichalcogenide semiconductors. 2D Mater. 2, 022001 (2015).

    Article  Google Scholar 

  37. 37.

    Ovesen, S. et al. Interlayer exciton dynamics in van der Waals heterostructures. Commun. Phys. 2, 23 (2019).

    Article  Google Scholar 

  38. 38.

    Selig, M. et al. Dark and bright exciton formation, thermalization, and photoluminescence in monolayer transtion metal dichalcogenides. 2D Mater. 5, 035017 (2018).

    Article  Google Scholar 

  39. 39.

    Yankowitz, M. et al. Emergence of superlattice Dirac points in graphene on hexagonal boron nitride. Nat. Phys. 8, 382–386 (2012).

    CAS  Article  Google Scholar 

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Acknowledgements

The authors thank M. Furthmeier for technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) through research training group GRK 1570, Collaborative Research Center SFB 1277 (projects A05 and B03) and project grant KO3612/3-1. The Chalmers group acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 696656 (Graphene Flagship) and the Swedish Research Council (VR).

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R.H. and E.M. supervised the study. P.M., F.M., P.S., A.G. and R.H. carried out the experiments. P.S., P.M., F.M., A.G., K.-Q.L., P.N., J.H., C.S., J.M.L. and T.K. prepared and pre-characterized the large-area heterostructures. S.O., S.B. and E.M. carried out the theoretical modelling. All authors analysed the data, discussed the results and contributed to the writing of the manuscript.

Corresponding authors

Correspondence to E. Malic or R. Huber.

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Supplementary Information

Supplementary Sections 1–6, Supplementary Figs. 1–6, Supplementary references 1–4.

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Merkl, P., Mooshammer, F., Steinleitner, P. et al. Ultrafast transition between exciton phases in van der Waals heterostructures. Nat. Mater. 18, 691–696 (2019). https://doi.org/10.1038/s41563-019-0337-0

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