Coupling-Induced Tunable Broadband Superradiance in 2D Metal-Dielectric-Metal Nanocavity Arrays

Subradiance/superradiance, cooperative effects causing suppressed/enhanced radiative decay, are of particular interest in plasmonic systems as they play a very important role in modulating dampings and optical properties of resonant systems. However, subradiance/superradiance are generally limited in narrow spectral range with inaccessible tunability. Realizing broadband subradiant and superradiant plasmon modes with flexible tuning is still challenging. Here, a 2D periodic multilayer metal-dielectric-metal (MDM) nanostructure is rationally designed and fabricated to realize a tunable superradiant mode over a broad visible range. Angle-resolved spectroscopy combined with full quantum calculations reveal a sufficient hybridization of delocalized guided plasmons with localized plasmons and a plasmonic cavity mode, leading to an emissive superradiant hybrid mode over a broadband visible range, which can be readily tuned by controlling the spectral three-mode overlap. Greatly shortened polariton lifetimes down to 4 fs are achieved as direct consequence of the Rabi phases and considerable incoherent coupling strengths between interacting subsystems. Such a control of plasmon damping by cooperative mode interactions paves the way toward efficient manipulation of light emission for applications requiring bright, fast-emitting photon sources.