Identification of spin, valley and moiré quasi-angular momentum of interlayer excitons

Abstract

Moiré superlattices provide a powerful way to engineer the properties of electrons and excitons in two-dimensional van der Waals heterostructures1,2,3,4,5,6,7,8. The moiré effect can be especially strong for interlayer excitons, where electrons and holes reside in different layers and can be addressed separately. In particular, it was recently proposed that the moiré superlattice potential not only localizes interlayer exciton states at different superlattice positions, but also hosts an emerging moiré quasi-angular momentum (QAM) that periodically switches the optical selection rules for interlayer excitons at different moiré sites9,10. Here, we report the observation of multiple interlayer exciton states coexisting in a WSe2/WS2 moiré superlattice and unambiguously determine their spin, valley and moiré QAM through novel resonant optical pump–probe spectroscopy and photoluminescence excitation spectroscopy. We demonstrate that interlayer excitons localized at different moiré sites can exhibit opposite optical selection rules due to the spatially varying moiré QAM. Our observation reveals new opportunities to engineer interlayer exciton states and valley physics with moiré superlattices for optoelectronic and valleytronic applications.

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Fig. 1: Interlayer moiré excitons in near-zero twist angle WSe2/WS2 heterostructure.
Fig. 2: Interlayer moiré excitons probed by helicity-resolved PLE spectroscopy.
Fig. 3: Interlayer moiré excitons probed by resonant pump–probe spectroscopy.

Data availability

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

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Acknowledgements

This work was supported primarily by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 (van der Waals heterostructures program, KCWF16). PLE spectroscopy of the heterostructure is supported by the US Army Research Office under MURI award W911NF-17-1-0312. The growth of hBN crystals was supported by the Elemental Strategy Initiative conducted by the MEXT, Japan and JSPS KAKENHI grant no. JP15K21722. S.T. acknowledges support from an NSF DMR 1552220 NSF CAREER award for the growth of WS2 and WSe2 crystals. E.C.R. acknowledges support from the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program. C.-S.Y. acknowledges support from grant no. 107-2112-M-003-014-MY3 from the Ministry of Science and Technology.

Author information

F.W. and C.J. conceived the research. C.J., E.C.R. and C.-S.Y. built the optical set-up. C.J., E.C.R. and D.W. carried out optical measurements. C.J., F.W. and E.C.R. performed theoretical analysis. E.C.R., D.W., M.I.B.U. and Z.Z. fabricated van der Waals heterostructures. Y.Q., Y.S., S.T., J.C. and A.Z. grew the WSe2 and WS2 crystals. K.W. and T.T. grew the hBN crystals. All authors discussed the results and wrote the manuscript.

Correspondence to Feng Wang.

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Peer review information: Nature Physics thanks Paulina Plochocka, Jun Yan and Ziliang Ye for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–4 and refs. 35–38.

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