Active control of excitonic strong coupling and electroluminescence in electrically driven plasmonic nanocavities

Enhancement and active control of light-matter interactions at the atomic scale is important for developing next-generation nanophotonic and quantum optical devices. Here, we demonstrate electric control of excitonic strong coupling and electroluminescence (EL) by integrating a semiconductor monolayer into a nanometer gap of single electrically driven nanocube-on-mirror plasmonic nanocavities, which provide unmatched optical and electrical confinement. In particular, in a strongly coupled system of nanocavity plasmons and tungsten diselenide (WSe₂) excitons, an ultrastrong electric field generated in the nanocavity gap enables reversible modulation of the Rabi splitting between ~108 and 102 milli-electron volts with a bias of only 2.5 volts. In the quantum tunneling regime (realized by decreasing the gap size), by injection of carriers into a nanocavity-integrated tungsten disulfide (WS₂) monolayer, spectrally tunable EL (controlled by the bias polarity) is achieved with a room-temperature quantum efficiency reaching ~3.5%, showing an improvement of more than 10³ times over previous works.