Topological transitions and surface umklapp scattering in Slack Metasurfaces

TL;DR

This paper introduces Slack Metasurfaces, which leverage structural degrees-of-freedom to control surface wave anisotropy and topological transitions, enabling novel wave manipulation such as backward focusing via umklapp processes.

Contribution

It presents a new class of metasurfaces that utilize all structural degrees-of-freedom to control wave propagation and topological transitions, expanding design possibilities beyond traditional deep-subwavelength approaches.

Findings

Controlled anisotropy of surface waves demonstrated

Observation of dual-stage topological transitions

Backward focusing of surface waves via umklapp process

Abstract

Metamaterials and metasurfaces are at the pinnacle of wave propagation engineering, yet their design has thus far been mainly focused on deep-subwavelength periodicities, practically forming an effective medium. Such an approach overlooks important structural degrees-of-freedom, e.g. the interplay between the corrugation periodicity and depth and how it affects the beam transport. Here, we present Slack Metasurfaces - weakly modulated metal-dielectric interfaces unlocking all structural degrees-of-freedom that affect the wave propagation. We experimentally demonstrate control over the anisotropy of surface waves in such metasurfaces, leading to yet, unexplored, dual stage topological transitions. We further utilize these metasurfaces to show unique backward focusing of surface waves driven by an umklapp process - momentum relaxation empowered by the periodic nature of the structure. Our findings can be applied to any type of guided waves, introducing a simple and diverse method for controlling wave propagation in artificial media.