  The manipulation of coupled quantum excitations is of fundamental importance
in realizing novel photonic and optoelectronic devices. We use
electroluminescence to probe plasmon-exciton coupling in hybrid structures
consisting of a nanoscale plasmonic tunnel junction and few-layer
two-dimensional transition-metal dichalcogenide transferred onto the junction.
The resulting hybrid states act as a novel dielectric environment that affects
the radiative recombination of hot carriers in the plasmonic nanostructure. We
determine the plexcitonic spectrum from the electroluminescence and find Rabi
splittings exceeding 50 meV in strong coupling regime. Our experimental
findings are supported by electromagnetic simulations that enable us to explore
systematically, and in detail, the emergence of plexciton polaritons as well as
the polarization characteristics of their far-field emission.
Electroluminescence modulated by plexciton coupling provides potential
applications for engineering compact photonic devices with tunable optical and
electrical properties.
