Complex exciton-plasmon coupling in WS2 coupled with different plasmonic cavities

Here, we report a comprehensive study on exciton-plasmon coupling in WS2 multilayers coupled with lithographically fabricated silver bowtie cavities, colloidal gold nanospheres, and silver nanocubes in multiple coupling geometries. Coupling a fixed number of WS2 layers with silver bowtie cavities leads to pronounced photoluminescence (PL) enhancement due to the Purcell effect, stimulated by strong electromagnetic field confinement within the bowtie cavity. Upon decreasing the bowtie gap size, this enhanced PL splits into two distinct peaks, a clear signature of strong exciton–plasmon coupling. The magnitude of this peak splitting can be further tuned by systematically reducing the gap size, thereby demonstrating tunability in our photonic system. Furthermore, WS2 coupled with gold nanospheres and silver nanocubes exhibits strong excitonic absorption, as well as polaritonic absorption features, depending on the number of layers involved in the interaction. Our comprehensive study reveals that the number of WS2 layers plays a crucial role in determining the dominant optical response, with plasmonic nanoparticles strongly assisting this effect. With fewer layers, PL enhancement is predominant, whereas increasing the number of layers leads to pronounced coupling between interlayer excitons and electromagnetic modes formed in self-hybridized Fabry-Pérot-type cavity modes, resulting in the formation of exciton-polaritons, further enhanced by plasmon coupling. Finite-difference time-domain (FDTD) simulations reveal the formation of self-hybridized exciton–polaritons in thick WS2 layers, together with the formation of in-plane closed-loop electric field distributions, a characteristic of an anapole mode. These numerical findings support our experimental observations and provide deeper insight into the underlying
–nanoparticle interactions.