Resonance Coupling between Molecular Excitons and Nonradiating Anapole Modes in Silicon Nanodisk-J-Aggregate Heterostructures

The nonradiating nature of anapole modes owing to the compositions of electric and toroidal dipole moments makes them distinct from conversional radiative resonances, and they have been suggested for the design of nanophotonic devices such as nanolasers based on light-matter interactions tailor by nanodisks. Therefore, the investigation of resonance coupling between molecular excitons and anapole modes is not only of fundamental interest, but is also promising for practical applications. To this end, a heterostructure composed of a silicon nanodisk and a uniform molecular J-aggregate ring is used to achieve the resonance coupling between the exciton transition and the anapole mode. In contrast with that of the conversional resonances, the resonance coupling is evidenced by a scattering peak around the exciton transition frequency, and the anapole mode splits into a pair of eigenmodes characterized as pronounced scattering dips, which are termed as the formation of two hybrid anapole modes caused by the coherent energy exchange in the heterostructure, and it has been verified by the multipole decompositions and the near-field distributions. An anticrossing behavior with a mode splitting of 161 meV is observed on the energy diagram, indicating that the strong coupling regime is achieved. Furthermore, due to the unique near-field distribution associated with the anapole mode, there is a much larger upper limit value for the width of the J-aggregate ring to enhance the resonance coupling, and the molecules located around the apexes of the disk perpendicular to the incident polarization play the dominate role for the resonance coupling.