Tailoring the Band Structure of Plexcitonic Crystals by Strong Coupling

Transition-metal dichalcogenides with their exciton-dominated optical behavior emerge as promising materials for realizing strong light-matter interactions in the visible range and at ambient conditions. When these materials are combined with metals, the energy confining ability of plasmon polaritons in metals below the diffraction limit allows for further enhancing and tailoring the light-matter interaction due to the formation of plexcitons in hybrid metal-TMDC structures at the interface. Herein, we demonstrate that the coupling between quasi-propagating plasmons in plasmonic crystals and excitons in WSe2 provides a multioscillator playground for tailoring the band structure of plasmonic crystal structures and results in emerging flat bands. The cathodoluminescence spectroscopy and angle-resolved measurements combined with the numerically calculated photonic band structure confirm a strong exciton-plasmon coupling, leading to significant changes in the band diagram of the hybrid lattice and the ability to tailor the band diagram via strong coupling. The hybrid plexcitonic crystal structures investigated here sustain optical waves with remarkably low group velocities. These results could be used for designing tunable slow-light structures based on the strong coupling effect and pave the way for plexcitonic topological photonic structures.

Automated summary

Transition-metal dichalcogenides combined with metals can enhance and tailor light-matter interactions, forming hybrid structures. The coupling between plasmons in plasmonic crystals and excitons in WSe2 results in flat bands, with optical waves exhibiting remarkably low group velocities. These findings have implications for the design of tunable slow-light structures and plexcitonic topological photonic structures.