Control of Plexcitonic Strong Coupling via Substrate-Mediated Hotspot Nanoengineering

Plexcitonic strong coupling has ushered in an era of room-temperature quantum electrodynamics at the nanoscale. Realizing its potential applications from single-molecule spectroscopy to room-temperature quantum technologies on an industrial level requires scalable and mass-producible plasmonic cavities that provide ease of access and control for quantum emitters. Here, a strategy for multidimensional hotspot engineering is proposed via a rational selection of substrates, which facilitates elevation of a gold bowtie nanocavity hotspot to the top of the device and provides a field enhancement of approximate to 482 (a 1.6-fold increase compared to a conventional bowtie-on-glass cavity at the bottom of the nanogap). The formation mechanism for these antenna modes is discussed from the perspective of charge carrier motion; and their advantages, particularly in view of their dominantly in-plane polarized near-fields, are further elaborated in a spatiotemporal study of plexcitonic strong coupling, which reveals ultrafast quantum dynamics and potential for applications related to 2D materials whose excitonic dipoles are typically oriented in-plane. The conceptual discovery of this substrate-enabled hotspot nanoengineering could readily be extended to tailor hotspots in other plasmonic platforms, and may inspire a plethora of novel research directions from plasmon-enhanced spectroscopy and sensing to the design of quantum logic gates and quantum metasurfaces.