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Every-other-layer dipolar excitons in a spin-valley locked superlattice

Abstract

Monolayer semiconducting transition metal dichalcogenides possess broken inversion symmetry and strong spin-orbit coupling, leading to a unique spin-valley locking effect. In 2H stacked pristine multilayers, spin-valley locking yields an electronic superlattice structure, where alternating layers correspond to barriers and quantum wells depending on the spin-valley indices. Here we show that the spin-valley locked superlattice hosts a kind of dipolar exciton with the electron and hole constituents separated in an every-other-layer configuration: that is, either in two even or two odd layers. Such excitons become optically bright via hybridization with intralayer excitons. This effect is also manifested by the presence of multiple anti-crossing patterns in the reflectance spectra, as the dipolar exciton is tuned through the intralayer resonance by an electric field. The reflectance spectra further reveal an excited state orbital of the every-other-layer exciton, pointing to a sizable binding energy in the same order of magnitude as the intralayer exciton. As layer thickness increases, the dipolar exciton can form a one-dimensional Bose–Hubbard chain displaying layer number-dependent fine spectroscopy structures.

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Fig. 1: Spin-valley locked superlattice and every-other-layer exciton.
Fig. 2: Electric field tuning of exciton hybridization.
Fig. 3: Stacking-dependent every-other-layer DX.
Fig. 4: Layer number dependence and multiple anti-crossings.

Data availability

Source data are provided with this paper. All other data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

References

  1. Bistritzer, R. & MacDonald, A. H. Moiré bands in twisted double-layer graphene. Proc. Natl Acad. Sci. USA 108, 12233–12237 (2011).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  3. Song, T. et al. Switching 2D magnetic states via pressure tuning of layer stacking. Nat. Mater. 18, 1298–1302 (2019).

    Article  CAS  Google Scholar 

  4. Li, T. et al. Pressure-controlled interlayer magnetism in atomically thin CrI3. Nat. Mater. 18, 1303–1308 (2019).

    Article  CAS  Google Scholar 

  5. Yasuda, K., Wang, X., Watanabe, K., Taniguchi, T. & Jarillo-Herrero, P. Stacking-engineered ferroelectricity in bilayer boron nitride. Science 372, 1458–1462 (2021).

    Article  CAS  Google Scholar 

  6. Woods, C. et al. Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride. Nat. Commun. 12, 347 (2021).

    Article  CAS  Google Scholar 

  7. Vizner Stern, M. et al. Interfacial ferroelectricity by van der Waals sliding. Science 372, 1462–1466 (2021).

    Article  CAS  Google Scholar 

  8. 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).

    Article  Google Scholar 

  9. Jones, A. M. et al. Spin–layer locking effects in optical orientation of exciton spin in bilayer WSe2. Nat. Phys. 10, 130–134 (2014).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  11. Wu, S. et al. Electrical tuning of valley magnetic moment through symmetry control in bilayer MoS2. Nat. Phys. 9, 149–153 (2013).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

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

    Article  Google Scholar 

  14. Gong, Z. et al. Magnetoelectric effects and valley-controlled spin quantum gates in transition metal dichalcogenide bilayers. Nat. Commun. 4, 2053 (2013).

    Article  Google Scholar 

  15. Shi, Q. et al. Bilayer WSe2 as a natural platform for interlayer exciton condensates in the strong coupling limit. Nat. Nanotechnol. 17, 577–582 (2022).

    Article  CAS  Google Scholar 

  16. Yankowitz, M., McKenzie, D. & LeRoy, B. J. Local spectroscopic characterization of spin and layer polarization in WSe2. Phys. Rev. Lett. 115, 136803 (2015).

    Article  Google Scholar 

  17. Bawden, L. et al. Spin-valley locking in the normal state of a transition-metal dichalcogenide superconductor. Nat. Commun. 7, 11711 (2016).

    Article  CAS  Google Scholar 

  18. Slobodeniuk, A. O. et al. Fine structure of K-excitons in multilayers of transition metal dichalcogenides. 2D Mater. 6, 025026 (2019).

    Article  CAS  Google Scholar 

  19. Liu, G.-B., Shan, W.-Y., Yao, Y., Yao, W. & Xiao, D. Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides. Phys. Rev. B 88, 085433 (2013).

    Article  Google Scholar 

  20. Wilson, N. R. et al. Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures. Sci. Adv. 3, e1601832 (2017).

    Article  Google Scholar 

  21. Król, M. et al. Exciton-polaritons in multilayer WSe2 in a planar microcavity. 2D Mater. 7, 015006 (2019).

    Article  Google Scholar 

  22. Arora, A. et al. Valley-contrasting optics of interlayer excitons in Mo- and W-based bulk transition metal dichalcogenides. Nanoscale 10, 15571–15577 (2018).

    Article  CAS  Google Scholar 

  23. Raiber, S. et al. Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2. Nat. Commun. 13, 4997 (2022).

    Article  CAS  Google Scholar 

  24. Shimazaki, Y. et al. Strongly correlated electrons and hybrid excitons in a moiré heterostructure. Nature 580, 472–477 (2020).

    Article  CAS  Google Scholar 

  25. Yoo, H. et al. Atomic and electronic reconstruction at the van der Waals interface in twisted bilayer graphene. Nat. Mater. 18, 448–453 (2019).

    Article  CAS  Google Scholar 

  26. Zhang, C. et al. Interlayer couplings, moiré patterns, and 2D electronic superlattices in MoS2/WSe2 hetero-bilayers. Sci. Adv. 3, e1601459 (2017).

    Article  Google Scholar 

  27. McGilly, L. J. et al. Visualization of moiré superlattices. Nat. Nanotechnol. 15, 580–584 (2020).

    Article  CAS  Google Scholar 

  28. Raja, A. et al. Coulomb engineering of the bandgap and excitons in two-dimensional materials. Nat. Commun. 8, 15251 (2017).

    Article  Google Scholar 

  29. Wang, Z., Zhao, L., Mak, K. F. & Shan, J. Probing the spin-polarized electronic band structure in monolayer transition metal dichalcogenides by optical spectroscopy. Nano Lett. 17, 740–746 (2017).

    Article  CAS  Google Scholar 

  30. Movva, H. C. et al. Density-dependent quantum Hall states and Zeeman splitting in monolayer and bilayer WSe2. Phys. Rev. Lett. 118, 247701 (2017).

    Article  Google Scholar 

Download references

Acknowledgements

This work was mainly supported by DoE BES (DE-SC0018171). Sample fabrication and PFM characterization were partially supported by the ARO MURI programme (W911NF-18-1-0431). The atomic force microscope-related measurements were performed using instrumentation supported by the US National Science Foundation through the UW Molecular Engineering Materials Center, a Materials Research Science and Engineering Center (DMR-1719797). W.Y. and C.X. acknowledge support from the University Grant Committee/Research Grants Council of Hong Kong SAR (AoE/P-701/20 and HKU SRFS2122-7S05). W.Y. also acknowledges support from the Tencent Foundation. Bulk WSe2 crystal growth and characterization by J.Y. were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. K.W. and T.T. acknowledge support from the JSPS KAKENHI (19H05790, 20H00354 and 21H05233). X.X. acknowledges support from the State of Washington-funded Clean Energy Institute and from the Boeing Distinguished Professorship in Physics.

Author information

Authors and Affiliations

Authors

Contributions

X.X. and W.Y. conceived the project. Y.Z. fabricated samples and performed measurements assisted by D.O., J.Z. and X.W. Y.Z., X.X., C.X. and W.Y. analysed and interpreted the results. C.X. and W.Y. performed calculations. T.T. and K.W. synthesized the hBN crystals. J.Y. synthesized and characterized the bulk WSe2 crystals. Y.Z., X.X., C.X. and W.Y. wrote the paper with input from all authors. All authors discussed the results.

Corresponding authors

Correspondence to Wang Yao or Xiaodong Xu.

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Extended data

Extended Data Fig. 1 Optical reflectance spectra in monolayer and bilayer WSe2.

a-b, Electric field (Ez) dependence of differential optical reflectance measurement in monolayer (a) and bilayer (b) WSe2. Doping is fixed at zero. As expected, the every-other-layer dipolar exciton as well as the anti-crossing feature are not observed.

Source data

Extended Data Fig. 2 Electric field EZ dependence of photoluminescence spectra in trilayer WSe2.

In addition to the dR/R data presented in the maintext, we examine photoluminescence (PL) spectra and its EZ field dependence on the same trilayer WSe2. Near K-K direct transition region (around 1.7 eV), we find similar anti-crossing feature as dR/R spectra, supporting the formation of every-other-layer dipolar excitons. The field-independent PL feature around 1.76 eV is instrument artefact.

Source data

Extended Data Fig. 3 Modeling and simulating the every-other-layer dipolar exciton.

a, EZ dependence of measured differential reflectance spectra in trilayer WSe2. The green dashed lines show the curve fitting results based on the Hamiltonian Eq. (2) + (3). b, Simulation results after considering the spectral intensity and width. c, d, Same plots for 5-layer WSe2.

Source data

Source data

Source Data Fig. 1

Statistical data for Fig. 1.

Source Data Fig. 2

Statistical data for Fig. 2.

Source Data Fig. 3

Statistical data for Fig. 3.

Source Data Fig. 4

Statistical data for Fig. 4.

Source Data Extended Data Fig.1

Statistical data for Extended Data Fig. 1.

Source Data Extended Data Fig. 2

Statistical data for Extended Data Fig. 2.

Source Data Extended Data Fig. 3

Statistical data for Extended Data Fig. 3.

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Zhang, Y., Xiao, C., Ovchinnikov, D. et al. Every-other-layer dipolar excitons in a spin-valley locked superlattice. Nat. Nanotechnol. 18, 501–506 (2023). https://doi.org/10.1038/s41565-023-01350-1

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