1 research outputs found
Toroidal Plasmonic Eigenmodes in Oligomer Nanocavities for the Visible
Plasmonics has become one of the most vibrant areas in
research
with technological innovations impacting fields from telecommunications
to medicine. Many fascinating applications of plasmonic nanostructures
employ electric dipole and higher-order multipole resonances. Also
magnetic multipole resonances are recognized for their unique properties.
Besides these multipolar modes that easily radiate into free space,
other types of electromagnetic resonances exist, so-called toroidal
eigenmodes, which have been largely overlooked historically. They
are strongly bound to material structures and their peculiar spatial
structure renders them practically invisible to conventional optical
microscopy techniques. In this Letter, we demonstrate toroidal modes
in a metal ring formed by an oligomer of holes. Combined energy-filtering
transmission electron microscopy and three-dimensional finite difference
time domain analysis reveal their distinct features. For the study
of these modes that cannot be excited by optical far-field spectroscopy,
energy-filtering transmission electron microscopy emerges as the method
of choice. Toroidal moments bear great potential for novel applications,
for example, in the engineering of Purcell factors of quantum-optical
emitters inside toroidal cavities