Optical nonlocality in polar dielectrics
Simone De Liberato, Christopher R. Gubbin
Abstract
Phonon polaritons localised in polar nanoresonators and superlattices are being actively investigated as promising platforms for mid-infrared nanophotonics. Here we show that the nonlocal nature of the phonon response can strongly modify their nanoscale physics. Using a nonlocal dielectric approach we study dielectric nanospheres and thin dielectric films taking into account optical phonons dispersion. We discover a rich nonlocal phenomenology, qualitatively different from the one of plasmonic systems. Our theory allows us to explain the recently reported discrepancy between theory and experiments in atomic-scale superlattices, and it provides a practical tool for the design of phonon-polariton nanodevices.