Plasmon-Exciton Strong\nCoupling in Single-Molecule\nJunction Electroluminescence

Single molecules bridging two metallic electrodes can\nemit light\nthrough electroluminescence when subjected to a bias voltage. Typically,\nlight emission in such devices results from transitions between molecular\nstates, although in the presence of light-matter coupling, the emission\ncan result from a transition between hybrid light-matter states. Here,\nwe create single metal-molecule-metal junctions and simultaneously\ncollect conductance and electroluminescence data using a scanning\ntunneling microscope (STM) equipped with a custom spectrometer. Through\nexperimental analysis and electronic structure calculations, we provide\nevidence for a molecule-electrode interfacial exciton coupled to a\njunction cavity plasmon. Importantly, we find that close to resonant\ntransport conditions, the molecular junction functions as a single\nemitter that is strongly coupled to the junction cavity mode, leading\nto characteristic Rabi splitting of the emission spectrum and providing\nthe first example of an electroluminescence-driven single-molecule\nsystem in the regime of strong light-matter coupling.