Probing strong exciton-plasmon coupling via hot-electron electroluminescence*

In electrically driven plasmonic tunnel junctions, electroluminescent emission can take place through the radiative recombination of hot electrons and holes, via the plasmon-modified photonic density of states.  We use this electroluminescence to probe plasmon- exciton coupling in hybrid structures, each consisting of a nanoscale plasmonic tunnel junction and few-layer WSe₂ flake transferred onto the junction. The coupling between the junction local surface plasmons and the excitons in the semiconductor leads to a photonic density of states with a strong plexcitonic splitting and polarization-dependent emission.  We use the above-threshold hot carrier electroluminescence to extract the photonic density of states and find Rabi splittings exceeding 50meV in strong coupling regime. Electromagnetic simulations explain the emergence of plexciton polaritons as well as the polarization characteristics of their far-field emission in the presence of other plasmon modes. Electroluminescence modulated by plexciton coupling is a promising approach for compact electrically driven light sources.