Speaker
Description
Phonon polaritons are hybrid light-matter quasiparticles in polar crystals that enable waveguiding of light on length scales much smaller than the photon wavelength [1]. Here, we introduce the hafnium dichalcogenides HfS2 and HfSe2 as new van der Waals materials that supports phonon polaritons in the terahertz (THz) spectral range. Using THz near-field optical microscopy coupled to the infrared free-electron laser facility FELBE [2] at the Helmholtz-Zentrum Dresden-Rossendorf, we demonstrate extreme confinement of light from 61 𝜇m free-space wavelength to 245 nm [3]. We show that the origin of this record-high confinement is an exceptionally large light-matter coupling of hyperbolic HfSe2. We also demonstrate hyperlensing as a means to verify the hyperbolicity of HfSe2. Our work opens up new avenues to deeply subdiffractional THz technologies [4].
[1] Galiffi et al., Nature Reviews Materials 9, 9 (2023)
[2] Helm et al., Eur. Phys. J. Plus 138 (2), 158 (2023)
[3] Kowalski et al., Nature Materials 24, 1735 (2025)
[4] Paarmann & Caldwell, Nature Materials 24, 1688 (2025)
| Scientific Topics | Imaging |
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