Light emission from a hybrid plasmonic-excitonic STM tunneling junction.

This work focuses on light emission from the nanojunction formed by the tip and a surface in a Scanning Tunneling Microscopy (STM) configuration. The nanojunction includes an ultrathin quantum well made of a single monolayer of a transition metal dichalcogenide material deposited on a gold surface. In this specific configuration, inelastic tunneling of electrons, induced by a bias voltage applied to the tip-surface gap of the STM, excites both Localized Surface Plasmon Polaritons (LSPPs) and excitons. These electromagnetic modes hybridize in this optical nanocavity, producing complex light emission spectra with both plasmonic and excitonic characteristics that depend on the tunneling parameters and the surface roughness. We model the luminescence process as radiative emission triggered by electron tunneling, and we estimate the quantum efficiency as the number of tunneling electrons required to initiate a single exciton recombination and subsequent photon emission. The calculated emission spectra describe the experimental observations well and allow for a thorough understanding of the fundamental physical processes behind light emission in a hybrid plasmonic-excitonic STM nanojunction.