Interface second harmonic generation enhancement in hetero-bilayer van der Waals nanoantennas

TL;DR

This paper demonstrates enhanced second harmonic generation at the interface of WS2/MoS2 hetero-bilayers using nanostructured antennas, revealing new opportunities for nanophotonic and nonlinear optical device design.

Contribution

It introduces a novel approach to enhance SHG in hetero-bilayer vdW materials through nanostructuring and resonant conditions, enabling up to 100-fold signal increase.

Findings

Up to 100-fold SHG enhancement observed.

Resonant excitonic and anapole conditions are key.

Interface of WS2/MoS2 hetero-bilayers enables SHG.

Abstract

Layered van der Waals (vdW) materials have emerged as a promising platform for nanophotonics due to large refractive indexes and giant optical anisotropy. Unlike conventional dielectrics and semiconductors, the absence of covalent bonds between layers allows for novel degrees of freedom in designing optically resonant nanophotonic structures down to the atomic scale, from the precise stacking of vertical heterostructures to controlling the twist angle between crystallographic axes. Specifically, while transition metal dichalcogenides monolayers exhibit giant second order nonlinear responses, their bulk counterparts with 2H stacking have zero second order response. In this work, we show second harmonic generation (SHG) arising from the interface of WS$_2$/MoS$_2$ hetero-bilayer thin films with an additional SHG enhancement in nanostructured optical antennas mediated by both the excitonic resonances and the anapole condition. When both conditions are met, we observe up to $10^2$ SHG signal enhancement. Our results highlights vdW materials as a platform for designing unique multilayer optical nanostructures and metamaterial, paving the way for advanced applications in nanophotonics and nonlinear optics.