Structural asymmetry and induced optical magnetism in plasmonic nanosandwiches
Journal article, 2008
A number of recent studies have shown that hybridized antiphase dipolar plasmons, qualitatively similar to
magnetic dipole resonances, can be excited in metal–dielectric–metal structures over a wide frequency range.
Here, we study how structural asymmetry in plasmonic nanosandwiches, composed of two Au disks separated
by a thin SiO2 layer, affects their near- and far-field optical properties using point-dipole analysis, electrodynamics
simulations, and optical spectroscopy. We find that the strength of the antiphase resonant mode can be
increased significantly compared to a symmetrical sandwich if the diameters or thicknesses of the nanodisks in
the sandwich are made to differ. Such asymmetrical nanosandwiches also exhibit a generally stronger magnetic
response, as characterized by the magnetic near-field enhancement in the region between the disks. However,
symmetry breaking also leads to pronounced directionality effects in the magnetic near-field, i.e., the enhancement
depends on which side of the sandwich that is first illuminated.