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Deep subwavelength topological edge state in a hyperbolic medium

Nature Nanotechnology volume 19, pages 1485–1490 (2024)Cite this article

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Abstract

Topological photonics offers the opportunity to control light propagation in a way that is robust from fabrication disorders and imperfections. However, experimental demonstrations have remained on the order of the vacuum wavelength. Theoretical proposals have shown topological edge states that can propagate robustly while embracing deep subwavelength confinement that defies diffraction limits. Here we show the experimental proof of these deep subwavelength topological edge states by implementing periodic modulation of hyperbolic phonon polaritons within a van der Waals heterostructure composed of isotopically pure hexagonal boron nitride flakes on patterned gold films. The topological edge state is confined in a subdiffraction volume of 0.021 µm3, which is four orders of magnitude smaller than the free-space excitation wavelength volume used to probe the system, while maintaining the resonance quality factor above 100. This finding can be directly extended to and hybridized with other van der Waals materials to broadened operational frequency ranges, streamline integration of diverse polaritonic materials, and compatibility with electronic and excitonic systems.

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Fig. 1: Device schematic and near-field measurements.
Fig. 2: Spectral and spatial near-field characterization of the edge state.
Fig. 3: Topological phase transition characterization.

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Data availability

The near-field raw experimental data that support the findings of this study are available via Zenodo at https://doi.org/10.5281/zenodo.11992364 (ref. 50).

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Acknowledgements

F.H.L.K. acknowledges support by the ERC TOPONANOP under grant agreement no. 726001, the Gordon and Betty Moore Foundation through Grant GBMF12212, project GRAFENOG, the Government of Spain (PID2019-106875GB-100; Severo Ochoa CEX2019-000910-S (MCIN/ AEI/10.13039/501100011033), PCI2021-122020-2A and PDC2022-133844-100 funded by MCIN/AEI/10.13039/501100011033), the European Union NextGenerationEU/PRTR (PRTR-C17.I1) and EXQIRAL 101131579, Fundació Cellex, Fundació Mir-Puig and Generalitat de Catalunya (CERCA, AGAUR, 2021 SGR 01443). Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union Research Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. Furthermore, the research leading to these results has received funding from the European Union’s Horizon 2020 under grant agreement no. 881603 (Graphene flagship Core3) and 820378 (Quantum flagship). This material is based upon work supported by the Air Force Office of Scientific Research under award number FA8655-23-1-7047. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force. L.O. acknowledges support by The Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya, as well as the European Social Fund (L’FSE inverteix en el teu futur)—FEDER. G.M.A. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101002955 – CONQUER). S.L. acknowledges the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (grant no. NRF-2023R1A2C1007836 and NRF-2020R1C1C1012138). J.H.E. and E.J. acknowledge the support for hBN crystals growth coming from the Office of Naval Research, award number N00014-22-1-2582. O.S. acknowledges the support of the Engineering and Physical Sciences Research Council (grant number EP/W005484). For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising. H.H.S. acknowledges funding from the European Union’s Horizon 2020 programme under the Marie Skłodowska-Curie grant agreement ref. 456 843830. M.C. acknowledges the support of the ‘Presencia de la Agencia Estatal de Investigación’ within the ‘Convocatoria de tramitación anticipada, correspondente al año 2020, de las ayudas para contractos predoctorales (ref. PRE2020-XXXXXX) para la formación de doctores contemplada en el Subprograma Estatal de Fromación del Programa Estatal de Promoción del Talento y su Empleabilidad en I + D + i, en el marco del Plan Estatal de Investigacón Científica y Técnica de Innovación 2017-2020, cofinanciado por el Fondo Social Europeo’. K.S. acknowledges the support from the European Commission in the Horizon 2020 Framework Programme under grant agreement nos. 785219 (Core2) and 881603 (Core3) of the Graphene Flagship. G.S. and Y.L. acknowledge the support of the Office of Naval Research (grant no. N00014-21-1-2056), the Army Research Office (grant no. W911NF-21-1-0180) and the National Science Foundation MRSEC programme (grant no. DMR-1719875).

Author information

Authors and Affiliations

  1. ICFO - Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Spain

    Lorenzo Orsini, Hanan Herzig Sheinfux, Matteo Ceccanti, Karuppasamy Soundarapandian & Frank H. L. Koppens

  2. Physics Department, Bar Ilan University, Ramat Gan, Israel

    Hanan Herzig Sheinfux

  3. School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA

    Yandong Li, Seojoo Lee & Gennady Shvets

  4. Department of Physics, Korea University, Seoul, Republic of Korea

    Seojoo Lee

  5. JEIP, USR 3573 CNRS, Collège de France, PSL Research University, Paris, France

    Gian Marcello Andolina

  6. Cavendish Laboratory, University of Cambridge, Cambridge, UK

    Orazio Scarlatella

  7. Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, USA

    Eli Janzen & James H. Edgar

  8. Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain

    Frank H. L. Koppens

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Contributions

L.O. and H.H.S. worked on sample fabrication with help from M.C. and K.S. Isotopic hBN crystals were grown by E.J. and J.H.E. Measurements and data analysis were performed by L.O. Simulations were performed by L.O. with help from Y.L. Theoretical support was provided by O.S., G.M.A., Y.L., S.L. and H.H.S. Experiments were designed by L.O., H.H.S and F.H.L.K. All authors contributed to writing the manuscript, and G.S. and F.H.L.K supervised the work.

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Correspondence to Frank H. L. Koppens.

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Nature Nanotechnology thanks Junsuk Rho and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Discussion, Figs. 1–9 and Tables 1 and 2.

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Orsini, L., Herzig Sheinfux, H., Li, Y. et al. Deep subwavelength topological edge state in a hyperbolic medium. Nat. Nanotechnol. 19, 1485–1490 (2024). https://doi.org/10.1038/s41565-024-01737-8

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