  Strong spatial confinement and highly reduced dielectric screening provide
monolayer transition metal dichalcogenides (TMDCs) with strong many-body
effects, thereby possessing optically forbidden excitonic states (i.e., dark
excitons) at room temperature. Herein, we explore the interaction of surface
plasmons with dark excitons in hybrid systems consisting of stacked gold
nanotriangles (AuNTs) and monolayer WS2. We observe a narrow Fano resonance
when the hybrid system is surrounded by water, and we attribute the narrowing
of the spectral Fano linewidth to the plasmon-enhanced decay of dark K-K
excitons. Our results reveal that dark excitons in monolayer WS2 can strongly
modify Fano resonances in hybrid plasmon-exciton systems and can be harnessed
for novel optical sensors and active nanophotonic devices.
