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Boundary-induced excitation of higher-order hyperbolic phonon polaritons

Nature Photonics (2025)Cite this article

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Abstract

Higher-order hyperbolic phonon polaritons (HoHPhPs), arising from photon–phonon coupling under geometric confinement and resonance conditions, exhibit larger wavevectors, field confinement and tunability compared with fundamental hyperbolic phonon polariton (HPhP) modes, making them promising for compact nanophotonic devices. However, their excitation remains challenging due to stringent momentum compensation requirements, leaving their properties and applications largely unexplored. Here we overcome this challenge by introducing a boundary-induced scattering mechanism that facilitates the efficient stepwise excitation of HoHPhPs. By creating a high-contrast dielectric environment with a gold–air hybrid substrate, we achieve substantial momentum compensation through scattering at the gold edge. Our approach is validated by theoretical analysis using dyadic Green’s function theory, demonstrating more than a sixfold increase in the excitation efficiency of HoHPhPs compared with conventional antenna-launching of HPhP. Experimentally, we observe HoHPhPs in α-MoO3 layers with a propagation distance of up to 15.2 μm and report a pseudo-birefringence effect with an ultrahigh equivalent birefringence ranging from 17.6 to 41.8. Thus, different polariton orders are spatially separated by their propagation direction without altering their polarization state. Our work introduces a novel strategy for the efficient excitation of HoHPhPs and establishes them as a versatile platform for nanophotonic applications such as mode routing in nanocircuits.

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Fig. 1: Two-step excitation of HoHPhPs.
Fig. 2: Real-space imaging of boundary-induced HoHPhP excitation using s-SNOM.
Fig. 3: Dispersion and loss analysis of HoHPhPs.
Fig. 4: Spatial separation of FPhPs and HoHPhPs via pseudo-birefringence.

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Data availability

The data that support the findings of this study are available in the Article and the Supplementary Information. Source data are provided with this paper.

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Acknowledgements

We acknowledge D. N. Basov (Columbia University) for valuable discussions and are grateful to X. Xi and X. Wang (State Key Laboratory of New Ceramics & Fine Processing, Tsinghua University) for scanning near-field optical microscopy measurements. The work was financially supported by the National Natural Science Foundation of China (grant numbers 52322209, 52172139 and 52350314 to H.H.), the National Key Research and Development Program of China (grant number 2021YFA1201500, to Q.D.), Beijing Nova Program (grant numbers 2022012 and 20240484600 to H.H.), Youth Innovation Promotion Association of Chinese Academy of Sciences (grant number 2022037 to H.H.), and the Postdoctoral Fellowship Program and China Postdoctoral Science Foundation (grant numbers BX20250181 and 2024M760685, to N.C.). R.H. acknowledges grant number CEX2020-001038-M funded by the Spanish MICIU/AEI/10.13039/50110001103 and grant number PID2021-123949OB-I00 funded by the Spanish MICIU/AEI/10.13039/501100011033 and ERDF/EU. F.J.G.A. acknowledges the ERC (grant number 789104-eNANO) and the Spanish MICINN (grant numbers PID2020-112625GB-I00 and SEV2015-0522).

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Author notes

  1. These authors contributed equally: Na Chen, Hanchao Teng.

Authors and Affiliations

  1. CAS Key Laboratory of Nanophotonic Materials and Devices, CAS Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing, People’s Republic of China

    Na Chen, Hanchao Teng & Hai Hu

  2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, People’s Republic of China

    Na Chen, Hanchao Teng & Hai Hu

  3. School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, People’s Republic of China

    Hanchao Teng & Qing Dai

  4. ICFO—Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels (Barcelona), Spain

    F. Javier García de Abajo

  5. ICREA—Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain

    F. Javier García de Abajo

  6. CIC nanoGUNE, Donostia-San Sebastián, Spain

    Rainer Hillenbrand

  7. CIC nanoGUNE BRTA and Department of Electricity and Electronics, UPV/EHU, Donostia-San Sebastián, Spain

    Rainer Hillenbrand

  8. IKERBASQUE, Basque Foundation for Science, Bilbao, Spain

    Rainer Hillenbrand

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  1. Na Chen
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Contributions

Q.D., R.H. and H.H. conceived the idea. Q.D., R.H. and F.J.G.A. supervised the project. N.C. and H.H. prepared the samples and conducted the near-field measurements. H.T. and F.J.G.A. developed the theoretical framework and performed the simulations. All authors contributed to the data analysis and discussion of the results. H.H., N.C. and H.T. co-wrote the manuscript with input and feedback from Q.D., R.H. and F.J.G.A.

Corresponding authors

Correspondence to Hai Hu, Rainer Hillenbrand or Qing Dai.

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Competing interests

R.H. is a co-founder of Neaspec GmbH, now part of attocube systems GmbH, a company that manufactures s-SNOM systems, including the one used in this study. The remaining authors declare no competing interests.

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Nature Photonics thanks Joshua Caldwell, William Wilson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–20 and Notes 1 and 2.

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Chen, N., Teng, H., Hu, H. et al. Boundary-induced excitation of higher-order hyperbolic phonon polaritons. Nat. Photon. (2025). https://doi.org/10.1038/s41566-025-01755-5

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