Spectral Tuning of Localized Surface Phonon Polariton Resonators for Low-Loss Mid-IR Applications

Low-loss surface phonon polariton (SPhP) modes supported within polar dielectric crystals are a promising alternative to conventional, metal-based plasmonic systems for the realization of nanophotonic components. Here we show that monopolar excitations in 4H-silicon carbide nanopillar arrays exhibit an unprecedented stable efficiency even when the resonator filling fraction is varied by an order of magnitude. This provides a powerful mid-IR platform with excellent spectral tunability and strong field confinement. Combining IR spectroscopy measurements with full electrodynamic calculations, we elucidate the nature of the optical modes in these elongated subwavelength nanostructures by investigating their spectral behavior and local field dependence on the size and periodicity. The present study also gives a clear understanding and practical guidelines for the spectral tuning of localized SPhP and the coupling mechanisms at play. This work is integral with the development of phonon-polariton based applications for surface-enhanced infrared absorption spectroscopy (SEIRA), polychromatic detectors, and thermal imaging.