Optical Nonlocality in Polar Dielectrics

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.

Impact of phonon nonlocality on nanogap and nanolayer polar resonators

“…To provide more agile approaches we recently developed an analytical continuum theory, describing polar nonlocality in terms of macroscopic fields. The validity of this model was confirmed by comparison to recent experiments for structures with features below 2nm in size 20,25 . Such analytical approaches are tractable in systems with strong symmetry but cannot be easily generalised.…”

“…The only inputs parameters required by the model, beyond those required for a local dielectric description, are the low-wavevector LO and TO phonon velocities which can be parameterised utilising the bulk phonon dispersions, readily available in the literature for most materials. The numerical approach is validated by comparison to our previous analytical nonlocal scattering spectra for 3C-SiC spheres 25 . The model is then applied to the study of spherical dimers, investigating the effect of nonlocality on field confinement.…”

“…In a previous publication 25 we solved Eq. 1 and Maxwell's equations analytically in simple systems of high symmetry: a sphere in vacuum and a suspended nanolayer.…”

“…We provided an exhaustive discussion of the appropriate ABC to be used in polar dielectrics in Ref. 25 , to which the interested reader is invited to refer. For completeness in the following we provide a brief overview of this important problem.…”

Macroscopic QED for quantum nanophotonics: emitter-centered modes as a minimal basis for multiemitter problems

“…[64], but can break down otherwise. In general, this happens for coupling to evanescent fields [65] and in particular when subwavelength confinement is used to generate extremely small effective mode volumes, such as in plasmonic [66,67] or phonon-polaritonic systems [68,69]. This observation is particularly relevant as such subwavelength confinement is the only possible strategy for obtaining large enough light-matter coupling strengths to approach the single-emitter strong coupling regime at room temperature [70][71][72][73].…”