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Polaritons are light-matter quasiparticles that govern the optical response of quantum materials and enable their nanophotonic applications1–4. We have studied a new type of polaritons arising in magnetized graphene5–7 encapsulated in hexagonal boron nitride (hBN)8–10. These polaritons arise from hybridization of Dirac magnetoexciton modes of graphene with waveguide phonon modes of hBN crystals. We refer to these quasiparticles as the Landau-phonon polaritons (LPPs). Using infrared magneto nanoscopy, we imaged LPPs and controlled their real-space propagation by varying the magnetic field. These LLPs have large in-plane momenta and are not bound by the conventional optical selection rules, granting us access to the “forbidden” inter-Landau level transitions (ILTs). We observed avoided crossings in the LPP dispersion – a hallmark of the strong coupling regime – occurring when the magnetoexciton and hBN phonon frequencies matched. Our LPP-based nanoscopy also enabled us to resolve two fundamental many-body effects: the graphene Fermi velocity renormalization11–16 and ILT-dependent magnetoexciton binding energies. These results indicate that magnetic-field-tuned Dirac materials, such as charge-neutral graphene, are promising platforms for precise nanoscale control of light-matter interaction.

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• Creative Commons BY-NC Attribution-NonCommercial 4.0 International
  

Keyword: Polaritons, Dirac magnetoexciton, hBN

Date published: 2024-09-13

Publisher: American Association for the Advancement of Science (AAAS)

Journal:

• Science Advances (ISSN: 23752548) vol. 10 issue. 37 eadp3487

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Manuscript type: Publisher's version (Version of record)

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First published URL: https://doi.org/10.1126/sciadv.adp3487

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Updated at: 2025-02-23 22:46:31 +0900

Published on MDR: 2025-02-23 22:46:31 +0900