Optical Rotation Reversal in the Optical Response of Chiral Plasmonic Nanosystems: The Role of Plasmon Hybridization

Chirality is an important molecular property for structural analysis. Similarly, it has been shown that plasmonic chiral systems exhibit strong circular dichroism (CD) responses that can be used to determine the relative positions of their constituent plasmonic elements. Here we show that the sign of the circular dichroism spectrum in a plasmonic system can be controllably changed through small geometric perturbations that change the energetic ordering of the hybridized modes. This mechanism is distinct from geometrical changes that explicitly change the handedness of the system. In a simple system composed of two stacked L-shaped resonators we observe a reversal of the optical rotation spectral signature for small relative shifts, and we show through electromagnetic modeling and experiments on lithographically patterned samples that this is due to a rearrangement of the relative energies between modes. The plasmonic system allows for geometric perturbation along controlled directions and therefore offers more control than corresponding molecular examples. Interestingly, this strong sensitivity in the optical response encodes more spatial information into the optical spectrum, emphasizing the importance of chiral plasmonic assemblies for structural investigations on the nanoscale.