  We demonstrate strong coupling between a single J-aggregate and an inverse
bowtie plasmonic structure, when the J-aggregate is located at a specific axial
distance from the metallic surface. Three hybrid modes are clearly observed,
witnessing a strong interaction, with a Rabi splitting of up to 290 meV, the
precise value of which significantly depends on the orientation of the
J-aggregate with respect to the symmetry axis of the plasmonic structure. We
repeated our experiments with a set of triangular hole arrays, showing
consistent formation of three or more hybrid modes, in good agreement with
numerical simulations.
