Hot-carrier induced giant above-threshold light emission enhancement in plasmonic tunnel junctions*

Surface plasmon enhanced processes and hot-carrier dynamics in plasmonic nanostructures have attracted much recent interest, revealing distinctive light-matter interactions at the nanoscale. By leveraging plasmonic tunnel junctions as a prototypical platform, recent works have reported enhanced light emission under simultaneous electrical and optical interband excitation at emitted photon energies below threshold (less than applied bias eV or incident photon energy). Here, based on the hot-carrier induced above-threshold electroluminescence, we report a surprising observation of Au nano junctions emitting over 1000-fold more upconverted photons under combined electrical and optical intraband excitation than the simple sum of light emission by either individual stimulus. Analysis of spectra shows that this enhancement is due to dramatic synergistic effects in the generation and interactions of plasmon-induced hot carriers under joint excitations. The observed giant cooperative effect in a plasmonic system may open great potential in on-chip nanophotonic switching, upconversion photovoltaics, and hot-carrier photocatalysis.