Plasmon‐Induced Optical Magnetism in an Ultrathin Metal Nanosphere‐Based Dimer‐on‐Film Nanocavity

Abstract

Recently, plasmon‐induced optical magnetism has attracted much research interest in nanophotonics and plasmonics due to intriguing applications in optical metamaterials, and ultrasensitive plasmonic nano‐metrology, among many others. Here, a strong in‐plane magnetic dipolar resonance in an ultrathin plasmonic nanocavity consisting of a silica‐coated gold nanosphere dimer coupled to a gold thin film is observed experimentally and explained theoretically. Multipolar expansion and numerical simulation disclose that such magnetic resonance is induced by a displacement current loop circulating around a nanometer thick triangular region in the cavity. The spectral response and radiation polarization of the magnetic mode are “visualized” by using a polarization‐resolved dark‐field imaging system at the single‐particle level. The resonance responses of this magnetic mode highly depends on cavity gap thickness, nanosphere dimension, and the incident angle, allowing straightforward resonance tuning from the visible to near‐infrared region and thus opening up a new avenue for magnetic resonance‐enhanced nonlinear optics and chiral optics.

Recent advances in plasmonic nanocavities for single-molecule spectroscopy

“…83 Other directions might include the combination of dimers and NPoM structures, so called dimers-on-lm, in order to obtain narrow resonances through the superposition of bright and dark modes. 84,85 DNA nanotechnology might also play a fundamental role in optimizing nanocavity hotspots. This paves the way for the combination of nanocavities with, for example, bio-assays for DNA sensing and diagnostics.…”

Light harvesting enhancement using metal nanoparticles

“…In [36], the field enhancement of spectroscopic measurements using metal nanostructures was demonstrated based on the nonlinear effect. In [37], the coupling between gold nanocavity and substrate was presented theoretically and experimentally. However, using different metal types like silver may give better optical performance based on optical coupling.…”

“…Mie theory and finite element method and finite difference time domain method have been deployed to show the key factors influencing the field enhancement. For instance, silver nanoparticles have been found to provide a better optical response than gold nanoparticles in terms of field intensity and distance between nanoparticles effect [37][38][39][40][41][42][43].…”

Enhanced Photoluminescence of Monolayer MoSe2 in a Double Resonant Plasmonic Nanocavity with Fano Resonance and Mode Matching

“…[ 18,30–32 ] Notice that with the large particle size or control of morphology, the PoM nanocavity can also support multipolar accessible resonances. [ 23,33,34 ] These high order modes, possessing more intense near field, are highly desirable to boost the excitation rate of PL. However, it remains scarce to fully exploit the benefit of the double resonance to augment both excitation and emission processes.…”