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Hyperbolic phonon polaritons (HPPs) are coupled oscillations of anisotropic lattice vibrations and electromagnetic fields that confine the latter to the nanoscale, enabling novel nano‐polaritonic devices. While HPPs have been identified in multiple layered materials, achieving advanced control and manipulation—particularly polariton canalization for unidirectional energy flow—often necessitates complex device fabrications or crystal modifications. Here we visualize and elucidate the properties of in‐plane hyperbolicity in α‐V2O5, a layered compound with a highly anisotropic permittivity tensor. We show unidirectional Poynting‐vector propagation of polaritons in α‐V2O5without additional treatments. Combined with theoretical modeling, our infrared nano‐imaging studies unveil a novel form of polariton canalization, with its dispersion contour continuously tunable by the incident light frequency. Additionally, we provide a theoretically calculated permittivity phase diagram for tailoring polaritonic wavefronts. These findings suggest that the metal‐oxide α‐V2O5holds great promise for on‐demand light canalization and control at the nanoscale.
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This content will become publicly available on February 1, 2027
Spectral Tuning of Hyperbolic Shear Polaritons in Monoclinic Gallium Oxide via Isotopic Substitution
ABSTRACT Hyperbolic phonon polaritons ‐ hybridized modes arising from the ultrastrong coupling of infrared light to strongly anisotropic lattice vibrations in uniaxial or biaxial polar crystals ‐ enable to confine light to the nanoscale with low losses and high directionality. In even lower symmetry materials, such as monoclinic ‐Ga2O3(bGO), hyperbolic shear polaritons (HShPs) further enhance the directionality. Yet, HShPs are intrinsically supported only within narrow frequency ranges defined by the phonon frequencies of the host material. Here, we report spectral tuning of HShPs in bGO by isotopic substitution. Employing near‐field optical microscopy to image HShPs in18O bGO films homoepitaxially grown on a16O bGO substrate, we demonstrate a spectral redshift of 40 cm−1for the18O bGO, compared to16O bGO. The technique allows for direct observation and a model‐free estimation of the spectral shift driven by isotopic substitution without the need for knowledge of the dielectric tensor. Complementary far‐field measurements and ab initio calculations ‐ in good agreement with the near‐field data ‐ confirm the effectiveness of this estimation. This multifaceted study demonstrates a significant isotopic substitution induced spectral tuning of HShPs into a previously inaccessible frequency range, creating new avenues for technological applications of such highly directional polaritons.
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- Award ID(s):
- 2236807
- PAR ID:
- 10685315
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 38
- Issue:
- 11
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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