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<p>While hyperbolic phonon-polaritons in van der Waals materials such as h-BN and <i>α</i>-MoO<sub>3</sub> have driven major advances in mid-infrared (IR) nanophotonics, further progress at longer THz wavelengths has been hampered due to material limitations and experimental challenges. Here, we report the discovery of long-lived hyperbolic phonon-polaritons in the deep THz range in layered PbI<sub>2</sub>. Using room-temperature scattering-type scanning near-field optical microscopy, we achieved real-space imaging and broadband spectral analysis of PbI<sub>2</sub> 2D crystals transferred onto different substrates with high near-field amplitude contrast and good agreement with theoretical models. Our measurements revealed an experimental figure-of-merit related to the propagating efficiency of the polaritons above 15—on par with state-of-the-art mid-IR benchmarks—and extreme field confinement of 264 for a 144 nm-thick flake, which can exceed 300 in slightly thinner samples. These findings demonstrate that PbI<sub>2</sub> combines strong anisotropy, low losses, and extreme mode confinement, making it a compelling candidate for deep-THz nanophotonic applications.</p>

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High quality-factor terahertz phonon-polaritons in layered lead iodide

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月4日

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  • Cristiane N. Santos,
  • Flávio H. Feres,
  • Théo Hannotte,
  • Romain Peretti,
  • Mathias Vanwolleghem,
  • Sophie Eliet,
  • Benjamin Walter,
  • Marc Faucher,
  • Adrian Cernescu,
  • Raul O. Freitas,
  • Jean-François Lampin

摘要

While hyperbolic phonon-polaritons in van der Waals materials such as h-BN and α-MoO3 have driven major advances in mid-infrared (IR) nanophotonics, further progress at longer THz wavelengths has been hampered due to material limitations and experimental challenges. Here, we report the discovery of long-lived hyperbolic phonon-polaritons in the deep THz range in layered PbI2. Using room-temperature scattering-type scanning near-field optical microscopy, we achieved real-space imaging and broadband spectral analysis of PbI2 2D crystals transferred onto different substrates with high near-field amplitude contrast and good agreement with theoretical models. Our measurements revealed an experimental figure-of-merit related to the propagating efficiency of the polaritons above 15—on par with state-of-the-art mid-IR benchmarks—and extreme field confinement of 264 for a 144 nm-thick flake, which can exceed 300 in slightly thinner samples. These findings demonstrate that PbI2 combines strong anisotropy, low losses, and extreme mode confinement, making it a compelling candidate for deep-THz nanophotonic applications.