Abstract
Phonon polaritons localized in polar nanoresonators and superlattices are being actively investigated as promising platforms for midinfrared 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.Received 9 December 2019Accepted 26 March 2020DOI:https://doi.org/10.1103/PhysRevX.10.021027Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNanophotonicsOptical phononsPhonon polaritonPhononsPhotonicsCondensed Matter, Materials & Applied Physics
Highlights
Nanophotonics is predicated on the ability to concentrate and control light on length scales substantially below the diffraction limit [1]
We study epsilon-near-zero (ENZ) resonances in aluminum nitride thin films and build on these results to model crystal hybrids composed of aluminum nitride (AlN)/gallium nitride (GaN) atomic-scale superlattices
Notwithstanding the technical similarities, we find that the impact of nonlocality on the optical response of phonon polaritons qualitatively differs from nonlocal plasmonics
Summary
Nanophotonics is predicated on the ability to concentrate and control light on length scales substantially below the diffraction limit [1]. Typical electromagnetic theories are parametrized by frequency-dependent dielectric functions in which a spatially local relationship between electric field and polarization is implicit. This approximation is known to fail in plasmonic systems of nanometric length scale [21,22], when longitudinal plasma waves induced in the electron gas by the transverse photon field at the particle boundary become. As SPhP concentrators grow smaller the dielectric local theory used to model them is expected to break down, as LO phonons hybridize with the photon field and perturb the system response. In this article we develop a macroscopic nonlocal theory describing the optical response of polar crystals. For the sake of clarity, most of the technical details of the calculations have been placed in the Appendixes
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