Onset of bonding plasmon hybridization preceded by gap modes in dielectric splitting of metal disks.

Dielectric splitting of nanoscale disks was studied experimentally and via finite-difference time-domain (FDTD) simulations through systematic introduction of multiple ultrathin dielectric layers. Tunable, hybridized dark bonding modes were seen with first-order gap modes preceding the appearance of bonding dipole-dipole disk modes. The observed bright dipolar mode did not show the energy shift expected from plasmon hybridization but activated dark higher order gap modes. Introducing lateral asymmetry was shown to remodel the field distribution resulting in 3D asymmetry that reoriented the dipole orientation away from the dipole of the elementary disk modes.