A crystal’s natural shape focuses light like a waveguide

Researchers have directly visualized the canalization of plasmon-polaritons in flakes of molybdenum oxychloride (MoOCl₂) without any fabrication or structuring. This intrinsic effect arises from the crystal's natural transition between elliptical and hyperbolic dispersion, allowing light to propagate in a highly directional, beam-like fashion at room temperature. The work extends canalized polariton propagation into the 4.5-6 μm range, a spectral region beyond existing phonon-polariton platforms and crucial for sensing important molecular vibrations, and demonstrates more than 1 μm of wavelength tunability simply by changing flake thickness. A naturally occurring crystal structure within molybdenum oxychloride (MoOCl₂) allows for the confinement and directional routing of light with…