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Infrared nano-imaging of Dirac magnetoexcitons in graphene

An Author Correction to this article was published on 17 November 2023

This article has been updated

Abstract

Magnetic fields can have profound effects on the motion of electrons in quantum materials. Two-dimensional electron systems subject to strong magnetic fields are expected to exhibit quantized Hall conductivity, chiral edge currents and distinctive collective modes referred to as magnetoplasmons and magnetoexcitons. Generating these propagating collective modes in charge-neutral samples and imaging them at their native nanometre length scales have thus far been experimentally elusive. Here we visualize propagating magnetoexciton polaritons at their native length scales and report their magnetic-field-tunable dispersion in near-charge-neutral graphene. Imaging these collective modes and their associated nano-electro-optical responses allows us to identify polariton-modulated optical and photo-thermal electric effects at the sample edges, which are the most pronounced near charge neutrality. Our work is enabled by innovations in cryogenic near-field optical microscopy techniques that allow for the nano-imaging of the near-field responses of two-dimensional materials under magnetic fields up to 7 T. This nano-magneto-optics approach allows us to explore and manipulate magnetopolaritons in specimens with low carrier doping via harnessing high magnetic fields.

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Fig. 1: Magnetic field-dependent m-SNOM and near-field photocurrent DiME measurements of hBN-encapsulated graphene at 200 K.
Fig. 2: Nano-infrared images of near-charge-neutral graphene in the regime of the field-tuned 0 → 1 LL transition.
Fig. 3: Magnetic field tuning of DiMEs.
Fig. 4: Magnetic field-dependent DiMEs dispersion.

Data availability

The data represented in Figs. 14 are available as Source Data 1–4. All other data that support the findings of this study are available from the corresponding authors upon reasonable request.

Code availability

All codes underlying this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

M.D., M.K.L. and Q.L. acknowledge support from the DOE, Office of Science, Basic Energy Sciences, Division of Materials Sciences and Engineering (Contract No. DE-SC0012704) for the construction of infrared optics and sample characterization. X.C., M.K.L and D.N.B. acknowledge the support of m-SNOM scanner construction as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the DOE, Office of Science, Basic Energy Sciences (Award DE-SC0019443). M.D., L.W., G.L.C, X.C, D.N.B. and M.K.L. acknowledge support of the Akiyama probe design from the US Department of Energy (DOE), Office of Science, National Quantum Information Science Research Centers, Co-design Center for Quantum Advantage (Contract No. DE-SC0012704). X.D. acknowledges support from the National Science Foundation (Award DMR-1808491). A.B.K. and A.B. are supported by the Swiss National Science Foundation (Grant No. 200020_201096). We are grateful for the helpful discussion and technical support from X. Xu at Lehigh University, D. Martien from Quantum Design, J. Li and W. Wang from Ithatron Optics, X. Wu from the Institute of Physics, Chinese Academy of Sciences, Q. Yang from Jilin University and Q. Sun from Tsinghua University.

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Contributions

M.D., M.T., X.C., L.W., W.Z., D.N.B. and M.K.L. designed the experiment. M.D., M.T., L.W., S.Z., X.D. and M.K.L. performed the measurements. X.D. and J.S. fabricated the samples. M.D., M.T., Z.D., X.C., L.W., W.Z. S.X., Y.D., V.R., M.P., Z.Z., A.B., G.L.C., Q.L., A.B.K., A.G., X.D., M.M.F. and M.K.L. analysed the data. M.T., X.C., W.Z., S.X., Y.S., R.J. and D.H. performed the simulations. M.D. and M.K.L wrote the paper. All authors contributed to the scientific discussions and paper revisions.

Corresponding authors

Correspondence to D. N. Basov, Xu Du or Mengkun Liu.

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Competing interests

M.D., X.C., M.K.L. and A.G. have a patent pending related to the design of the m-SNOM. The other authors declare no competing interests.

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Extended data

Extended Data Fig. 1 Closed-cycle m-SNOM setup.

OAP: off-axis parabolic mirror. Tip: Akiyama probe. Light enters the chamber in the horizontal direction (into the field of view) and is focused onto the sample with an OAP.

Supplementary information

Supplementary Information

Supplementary Notes 1–3 and Figs. 1–8.

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Source data

Source Data Fig. 1

Source data for Fig. 1d–f.

Source Data Fig. 2

Source data for Fig. 2a,b.

Source Data Fig. 3

Source data for Fig. 3b–d.

Source Data Fig. 4

Source data for Fig. 4a–d.

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Dapolito, M., Tsuneto, M., Zheng, W. et al. Infrared nano-imaging of Dirac magnetoexcitons in graphene. Nat. Nanotechnol. 18, 1409–1415 (2023). https://doi.org/10.1038/s41565-023-01488-y

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