  Surface plasmon enhanced processes and hot-carrier dynamics in plasmonic
nanostructures are of great fundamental interest to reveal light-matter
interactions at the nanoscale. Using plasmonic tunnel junctions as a platform
supporting both electrically- and optically excited localized surface plasmons,
we report a much greater (over 1000x) plasmonic light emission at upconverted
photon energies under combined electro-optical excitation, compared with
electrical or optical excitation separately. Two mechanisms compatible with the
form of the observed spectra are interactions of plasmon-induced hot carriers
and electronic anti-Stokes Raman scattering. Our measurement results are in
excellent agreement with a theoretical model combining electro-optical
generation of hot carriers through non-radiative plasmon excitation and
hot-carrier relaxation. We also discuss the challenge of distinguishing
relative contributions of hot carrier emission and the anti-Stokes electronic
Raman process. This observed increase in above-threshold emission in plasmonic
systems may open avenues in on-chip nanophotonic switching and hot carrier
photocatalysis.
