Single Photon Emission from a Plasmonic Light Source Driven by a Local Field-Induced Coulomb Blockade

A hallmark of quantum control is the ability to manipulate quantum emission at the nanoscale. Through scanning tunneling microscopy-induced luminescence (STML), we are able to generate plasmonic light originating from inelastic tunneling processes that occur in the vacuum between a tip and a few-nanometer-thick molecular film of C-60 deposited on Ag(111). Single photon emission, not of molecular excitonic origin, occurs with a 1/e recovery time of a tenth of a nanosecond or less, as shown through Hanbury Brown and Twiss photon intensity interferometry. Tight-binding calculations of the electronic structure for the combined tip and Ag-C-60 system results in good agreement with experiment. The tunneling happens through electric-field-induced split-off states below the C-60 LUMO band, which leads to a Coulomb blockade effect and single photon emission. The use of splitoff states is shown to be a general technique that has special relevance for narrowband materials with a large bandgap.