Chiral Plasmonic Ellipsoids: An Extended Mie-Gans Model.

Mie-Gans theory optically characterizes ellipsoidal and by extension generally elongated nonchiral metal nanoparticles (MNPs) and is ubiquitous in verifying experimental results and predicting particle behavior. Recently, elongated chiral MNPs have garnered enthusiasm, but a theory to characterize their chiroptical behavior is lacking in the literature. In this Letter, we present an model for chiral ellipsoidal MNPs to address this shortcoming and demonstrate that it reduces to the general Mie-Gans model under nonchiral conditions, produces results that concur with state-of-the-art numerical simulations, and can accurately replicate recent experimental measurements. Furthermore, to gain physical insights, we analyze factors such as background medium permittivity and particle size that drive the chiroptical activity using two types of plasmonic chiral MNPs. We also demonstrate the utility of our model in metamaterial design. Generic features of our model can be extended to characterize similar elongated chiral MNPs, fueling many other variants of the current model.