Exquisite control of the coherent interaction between a plasmonic mode and a single molecule with sub-nanometer spatial resolution has been demonstrated in the field of nanophotonics. The result has been published in Nature Communications.
Researchers from the Theory of Nanophotonics group at the Centro de Física de Materiales and the Donostia International Physics Center in San Sebastian, together with collaborators in the University of Science and Technology of China in Hefei, have studied theoretically and experimentally the optical response of a molecule that is situated near a silver Scanning Tunneling Microscope (STM) tip working at cryogenic temperature. When the molecule is displaced slightly out of the plasmonic cavity, the coherent ‘back-and-forth’ interaction between molecule and plasmonic cavity results in very characteristic Fano profiles of the emission. By tracking the changes in the Fano profile as the tip is displaced, it was possible to demonstrate a strong localization of the electromagnetic field to a plasmonic hot-spot of ≈1nm of lateral size and, as a consequence, to control the coherent plasmon-molecule coupling with sub-nanometer resolution. Furthermore, this interaction also leads to changes in the energy of the molecular transition due to the so-called photonic Lamb shift.