Strong light-matter interaction with self-hybridized bound states in the continuum in monolithic van der Waals metasurfaces

TL;DR

This paper demonstrates monolithic van der Waals metasurfaces with bound states in the continuum (BICs) that enable strong light-matter coupling, tunable resonances, and control over Rabi splitting, advancing nanophotonic device capabilities.

Contribution

It introduces the first experimental realization of asymmetry-dependent BIC resonances in monolithic TMDC WS$_2$ metasurfaces, enabling precise control of light-matter interactions.

Findings

Achieved sharp, tunable BIC resonances in monolithic WS$_2$ metasurfaces.

Observed strong coupling with a Rabi splitting of 116 meV.

Controlled Rabi splitting via geometrical asymmetry, independent of material losses.

Abstract

Photonic bound states in the continuum (BICs) are a standout nanophotonic platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs), but have so far mostly been employed as all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap, and material integration. In this work, we experimentally demonstrate for the first time asymmetry-dependent BIC resonances in 2D arrays of monolithic metasurfaces composed solely of the nanostructured bulk TMDC WS$_2$ with BIC modes exhibiting sharp and tailored linewidths, ideal for selectively enhancing light-matter interactions. Geometrical variation enables the tuning of the BIC resonances across the exciton resonance in bulk WS$_2$, revealing the strong-coupling regime with an anti-crossing pattern and a Rabi splitting of 116 meV. The precise control over the radiative loss channel provided by the BIC concept is harnessed to tailor the Rabi splitting via a geometrical asymmetry parameter of the metasurface. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our BIC-driven monolithic metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver previously unavailable fundamental insights and practical device concepts for polaritonic applications.