Tuning light at the nanoscale through isotopic engineering
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An international research team led by the Fritz Haber Institute of the Max Planck Society, the Paul Drude Institute for Solid State Electronics (PDI), and the University of Iowa has demonstrated a new way to control how light behaves at extremely small scales by changing the atomic composition of a material.
In a study published in Advanced Materials, the researchers show that replacing oxygen atoms in monoclinic gallium oxide (β-Ga₂O₃) with a heavier oxygen isotope shifts the spectral range of hyperbolic shear polaritons, a special type of light–matter excitation in low symmetry crystals that combines light with vibrations of the crystal lattice. These polaritons can guide infrared light along highly directional paths at dimensions far below the wavelength of light itself.
Crucially, the team found that isotopic substitution moves the polariton resonances into previously inaccessible frequency ranges, while leaving their propagation behaviour essentially unchanged. This is important because, in many nanophotonic systems, tuning the operating frequency typically comes at the cost of increased losses or altered performance. Here, the spectral position can be adjusted without compromising functionality.
The effect was observed directly using advanced infrared nano-imaging techniques and confirmed through complementary far-field spectroscopy and theoretical modelling. By modifying the crystal’s atomic mass rather than its structure or geometry, the approach provides a robust and material-intrinsic way to tailor light–matter interactions, without relying on complex external control schemes.
Researchers at PDI played a key role by growing high-quality β-Ga₂O₃ layers with controlled isotopic composition, providing the foundation for the experimental studies. Together with the combined expertise across the collaboration, this work demonstrates how atomic-scale material engineering can open new degrees of freedom in nanophotonics.
The results pave the way for more versatile infrared optical components, such as compact waveguides, sensors, and on-chip photonic devices, and highlight isotopic engineering as a powerful new tool for controlling light at the nanoscale.
Title: Spectral tuning of hyperbolic shear polaritons in monoclinic gallium oxide via isotopic substitution
Authors: G. Carini, M. Pradhan, E. Gelžinytė, A. Ardenghi, S. Dixit, M. Obst, A. S. Senarath, N. S. Mueller, G. Álvarez-Pérez, K. Diaz-Granados, R. A. Kowalski, R. Niemann, F. G. Kaps, J. Wetzel, R. B. Iyer, P. Mazzolini, M. Schubert, J. M. Klopf, J. T. Margraf, O. Bierwagen, M. Wolf, K. Reuter, L. M. Eng, S. C. Kehr, J. D. Caldwell, C. Carbogno, T. G. Folland, M. R. Wagner, A. Paarmann
Source: Adv. Mater., tba, e14561 (2026)
DOI: 10.1002/adma.202514561