Subradiant, superradiant and Fano resonances in dimer and ring/disk nanocavities

Abstract

Subradiant and superradiant plasmon modes in ring/disk nanocavities and dialers are investigated theoretically and experimentally. The subradiance is obtained through an overall reduction of the total dipole moment of the hybridized mode due to antisymmetric coupling of the dipole moments of the parent plasmons. We observe the appearance of Fano resonances in the optical response of plasmonic nanocavities due to the coherent coupling between their superradiant and subradiant plasmon modes due to structural symmetry breaking. Both subradiant modes and Fano resonances exhibit substantial reductions in linewidth compared to the parent plasmon resonances, opening up possibilities in optical and near IR sensing via plasmon lineshape design. Four reduced-symmetry nanostructures Studied via Plasmon Hybridization and FDTD (Finite Difference Time Domain), a dolmen-style slab arrangement, a ring/disk dimer, a ring/disk cavity and a colloid dimer, clearly exhibit the strong polarization and geometry dependence expected for this behavior at the individual nanostructure level, confirmed by experimental result in each case, multiple Fano resonances occur as structure size is increased.