Broadband Unidirectional Scattering by Magneto-Electric Core–Shell Nanoparticles

Abstract

Core-shell nanoparticles have attracted surging interests due to their flexibly tunable resonances and various applications in medical diagnostics, biosensing, nanolasers, and many other fields. The core-shell nanoparticles can support simultaneously both electric and magnetic resonances, and when the resonances are properly engineered, entirely new properties can be achieved. Here we study core-shell nanoparticles that support both electric and artificial magnetic dipolar modes, which are engineered to coincide spectrally with the same strength. We reveal that the interferences of these two resonances result in azimuthally symmetric unidirectional scattering, which can be further improved by arranging the nanoparticles in a chain, with both azimuthal symmetry and vanishing backward scattering preserved over a wide spectral range. We also demonstrate that the vanishing backward scattering is preserved, even for random particle distributions, which can find applications in the fields of nanoantennas, photovoltaic devices, and nanoscale lasers that require backward scattering suppressions.

Directional visible light scattering by silicon nanoparticles

“…This results from spectral overlap of electric and magnetic dipole resonances and leads to an increase of the total scattering in the forward direction. Similar effects were recently theoretically predicted for silver core/silicon shell nanoparticles where overlapping of electric and magnetic resonance was achieved by changing the size of the silver core 19 .…”

“…One of the possible ways to avoid such limitation and still have similar resonant properties is to use high-refractive index dielectric nanoparticles 15,16 . Recently, visible-range nanoantennas based on spherical silicon nanoparticles have been theoretically analysed demonstrating higher efficiency compared with their metallic analogues [17][18][19] . However, experimental demonstrations of such antennas have been limited to millimetre scales and microwave frequencies 20 .…”

Magnetic and electric coherence in forward- and back-scattered electromagnetic waves by a single dielectric subwavelength sphere

“…The increasing demand of wireless device miniaturization for communication and sensor applications, and the search of new materials with electromagnetic properties 'à la carte', has fostered a renewed interest in subwavelength particles as basic building blocks for controlling optical radiation at subwavelength scales. These issues underline the emerging concepts of metamaterial inspired microwave and radio-wave electrically small antennas 4 and their optical analogues, either dielectric 5,6 or based on plasmon subwavelength optics 7 .…”

“…26). An all-dielectric Yagi-Uda antenna based on these ideas was recently proposed 6,30 and experimentally tested in the microwave regime 31 . The scattering anisotropy also has a key role in the mechanical action of electromagnetic fields on small particles.…”

Boosting Fano resonances in single layered concentric core–shell particles

“…Figure 7.a shows the efficiencies of a silvercore silicon-shell particle with r c = 68 nm and r s = 225 nm surrounded by air. This particle configuration has been recently proposed as a structure able to achieve broadband unidirectional scattering response thanks to the combination of the electric dipole moment from the silver core and the magnetic dipole moment of the silicon shell that are excited in the same spectral region 75 . This characteristic is illustrated in the radiation pattern at the resonance peak (Fig 7.c).…”