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Moiré trions in MoSe2/WSe2 heterobilayers

Abstract

Transition metal dichalcogenide moiré bilayers with spatially periodic potentials have emerged as a highly tunable platform for studying both electronic1,2,3,4,5,6 and excitonic4,7,8,9,10,11,12,13 phenomena. The power of these systems lies in the combination of strong Coulomb interactions with the capability of controlling the charge number in a moiré potential trap. Electronically, exotic charge orders at both integer and fractional fillings have been discovered2,5. However, the impact of charging effects on excitons trapped in moiré potentials is poorly understood. Here, we report the observation of moiré trions and their doping-dependent photoluminescence polarization in H-stacked MoSe2/WSe2 heterobilayers. We find that as moiré traps are filled with either electrons or holes, new sets of interlayer exciton photoluminescence peaks with narrow linewidths emerge about 7 meV below the energy of the neutral moiré excitons. Circularly polarized photoluminescence reveals switching from co-circular to cross-circular polarizations as moiré excitons go from being negatively charged and neutral to positively charged. This switching results from the competition between valley-flip and spin-flip energy relaxation pathways of photo-excited electrons during interlayer trion formation. Our results offer a starting point for engineering both bosonic and fermionic many-body effects based on moiré excitons14.

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Fig. 1: Moiré trions are formed with electrostatic gating.
Fig. 2: Zeeman splitting of both neutral and charged moiré excitons.
Fig. 3: Doping-dependent valley polarization of moiré trions.
Fig. 4: Moiré exciton and trion dynamics.

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.

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Acknowledgements

Research on moiré trions is primarily supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award DE-SC0019443. Zeeman-splitting and time-resolved measurements are mainly supported by DoE BES under award DE-SC0018171. Device fabrication is partially supported by the Army Research Office (ARO) Multidisciplinary University Research Initiative (MURI) Program (grant no. W911NF-18-1-0431) and the NSF EFRI (grant no. 1741656). The AFM-related measurements were performed using instrumentation supported by the US National Science Foundation through the UW Molecular Engineering Materials Center (MEM·C), a Materials Research Science and Engineering Center (DMR-1719797). W.Y. and H.Z. acknowledge support from the Croucher Foundation (Croucher Senior Research Fellowship) and the University Grant Committee/Research Grants Council of Hong Kong SAR (AoE/P-701/20). D.G.M. and J.Y. are 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 Elemental Strategy Initiative conducted by MEXT, Japan (grant no. JPMXP0112101001), JSPS KAKENHI (grant no. JP20H00354) and CREST (JPMJCR15F3), JST. X.X. acknowledges the support from the State of Washington funded Clean Energy Institute and from the Boeing Distinguished Professorship in Physics.

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Contributions

X.X. and W.Y. conceived the experiment. X.W. and J.Z. fabricated the samples, assisted by Y.W. and M.H. The measurements were performed by X.W. and J.Z. Device D2 was fabricated and measurements were performed by K.L.S. and P.R. The results were analysed and interpreted by X.W., J.Z., H.Z. X.X., W.Y. and D.R.G. Crystals of BN were synthesized by T.T. and K.W. Bulk WSe2 and MoSe2 crystals were synthesized and characterized by J.Y. and D.G.M. The paper was written by X.W., X.X., W.Y. and D.R.G. with input from all authors. All authors discussed the results.

Corresponding authors

Correspondence to Wang Yao or Xiaodong Xu.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Igor Bondarev, Libai Huang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Text and Figs. 1–8.

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Wang, X., Zhu, J., Seyler, K.L. et al. Moiré trions in MoSe2/WSe2 heterobilayers. Nat. Nanotechnol. (2021). https://doi.org/10.1038/s41565-021-00969-2

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