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Spectral Tuning of Hyperbolic Shear Polaritons in Monoclinic Gallium Oxide via Isotopic Substitution

Carini, Giulia ; Pradhan, Mohit ; Gelžinytė, Elena ; Ardenghi, Andrea ; Dixit, Saurabh ; Obst, Maximilian ; Senarath, Aditha S. ; Mueller, Niclas S. ; Álvarez-Pérez, Gonzalo and Diaz-Granados, Katja , et al. (2026) In Advanced Materials 38(11).
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 (Formula presented.) -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 in 18O bGO films... (More)

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 (Formula presented.) -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 in 18O bGO films homoepitaxially grown on a 16O bGO substrate, we demonstrate a spectral redshift of (Formula presented.) 40 cm−1 for the 18O bGO, compared to 16O 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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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
DFT calculations, FT-IR, isotopic substitution, near-field microscopy, shear polaritons
in
Advanced Materials
volume
38
issue
11
article number
e14561
publisher
John Wiley & Sons Inc.
external identifiers
  • scopus:105027392095
  • pmid:41518292
ISSN
0935-9648
DOI
10.1002/adma.202514561
language
English
LU publication?
yes
id
d87fe1a4-30ed-4f1d-bf1b-a1f3ffec8bfc
date added to LUP
2026-03-16 15:38:03
date last changed
2026-03-17 03:00:03
@article{d87fe1a4-30ed-4f1d-bf1b-a1f3ffec8bfc,
  abstract     = {{<p>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 (Formula presented.) -Ga<sub>2</sub>O<sub>3</sub> (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 in <sup>18</sup>O bGO films homoepitaxially grown on a <sup>16</sup>O bGO substrate, we demonstrate a spectral redshift of (Formula presented.) 40 cm<sup>−1</sup> for the <sup>18</sup>O bGO, compared to <sup>16</sup>O 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.</p>}},
  author       = {{Carini, Giulia and Pradhan, Mohit and Gelžinytė, Elena and Ardenghi, Andrea and Dixit, Saurabh and Obst, Maximilian and Senarath, Aditha S. and Mueller, Niclas S. and Álvarez-Pérez, Gonzalo and Diaz-Granados, Katja and Kowalski, Ryan A. and Niemann, Richarda and Kaps, Felix G. and Wetzel, Jakob and Iyer, Raghunandan Balasubramanyam and Mazzolini, Piero and Schubert, Mathias and Klopf, J. Michael and Margraf, Johannes T. and Bierwagen, Oliver and Wolf, Martin and Reuter, Karsten and Eng, Lukas M. and Kehr, Susanne C. and Caldwell, Joshua D. and Carbogno, Christian and Folland, Thomas G. and Wagner, Markus R. and Paarmann, Alexander}},
  issn         = {{0935-9648}},
  keywords     = {{DFT calculations; FT-IR; isotopic substitution; near-field microscopy; shear polaritons}},
  language     = {{eng}},
  month        = {{02}},
  number       = {{11}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{Advanced Materials}},
  title        = {{Spectral Tuning of Hyperbolic Shear Polaritons in Monoclinic Gallium Oxide via Isotopic Substitution}},
  url          = {{http://dx.doi.org/10.1002/adma.202514561}},
  doi          = {{10.1002/adma.202514561}},
  volume       = {{38}},
  year         = {{2026}},
}