Enhanced Magnetic and Electric Fields via Fano Resonances in Metasurfaces of Circular Clusters of Plasmonic Nanoparticles

We investigate for the first time the capacity of a two-dimensional periodic array (a metasurface) of circular nanoclusters (CNCs) of plasmonic nanoparticles to support magnetic Fano resonances. These resonances are characterized by narrow angular and/or spectral features in the reflection/transmission/absorption coefficients associated with a circular disposition of nanoparticles' dipole moments (forming a current loop) under oblique TE-polarized plane wave incidence illumination. We find that these narrow resonant features are either array-induced or single-CNC-induced, as shown by using a theoretical analysis based on the single dipole approximation and full-wave simulations, leading to enhanced magnetic and electric fields. In particular, array-induced resonances are narrower than single-CNC-induced ones and also provide even larger field enhancements, in particular generating a magnetic field enhancement of about 10-fold and an electric field enhancement of about 40-fold for a representative metasurface. We suggest that the novel results pertaining to metasurfaces made of CNCs shown here may be used for the development of sensors based on enhanced magnetic fields and for the enhancement of magnetic nonlinearities. (Chemical Equation Presented).