Near-field infrared nanospectroscopy of surface phonon-polariton resonances

P. McArdle, D. J. Lahneman, A. Biswas, F. Keilmann and M. M. Qazilbash

Phys. Rev. Research 2, 023272 (2020)
We present combined experimental and numerical work on light-matter interactions at nanometer length scales. We report numerical simulations of near-field infrared nanospectroscopy that consider detailed tip geometry and have no free parameters. Our results match published spectral shapes of amplitude and phase measurements even for strongly resonant surface phonon-polariton (SPhP) modes. They also verify published absolute scattering amplitudes. A unique, ultrabroadband light source enables near-field amplitude and phase acquisition into the far-infrared spectral range. This allowed us to discover a strong SPhP resonance in the polar dielectric SrTiO3 (STO) at an ∼24 μm wavelength of incident light.