  We study fluctuations in plasmonic electroluminescence at the single-atom
limit profiting from the precision of a low-temperature scanning tunneling
microscope. First, we investigate the influence of a controlled single-atom
transfer on the plasmonic properties of the junction. Next, we form a
well-defined atomic contact of several quanta of conductance. In contact, we
observe changes of the electroluminescence intensity that can be assigned to
spontaneous modifications of electronic conductance, plasmonic excitation and
optical antenna properties all originating from minute atomic rearrangements at
or near the contact. The observations are relevant for the understanding of
processes leading to spontaneous intensity variations in plasmon-enhanced
atomic-scale spectroscopies.
