Acoustic wave modulation of gap plasmon cavities

The role of metallic nanostructures in nanophotonics is expected to expand if ways to electrically manipulate their optical resonances at high speed can be identified. Here, we capitalize on electrically-driven surface acoustic waves and the extreme light concentration afforded by gap plasmons to achieve this goal. We place gold nanoparticles in a particle-on-mirror configuration with a few-nanometer-thick, compressible polymer spacer. Surface acoustic waves are then used to tune light scattering at speeds approaching the GHz regime. We observe evidence that the surface acoustic waves produce mechanical deformations in the polymer, and that ensuing nonlinear mechanical dynamics lead to unexpectedly large levels of strain and spectral tuning. Our approach provides a design strategy for electrically driven dynamic metasurfaces and fundamental explorations of high-frequency, polymer dynamics in ultra-confined geometries.