Colloidal Solutions of Silicon Nanospheres toward All-Dielectric Optical Metafluids

A colloidal
solution of nanophotonic structures exhibiting optical
magnetism is dubbed a liquid-phase metamaterial or an optical metafluid.
Over the decades, plasmonic nanoclusters have been explored as constituents
of a metafluid. However, optical magnetism of plasmonic nanoclusters
is usually much weaker than the electric responses; the highest reported
intensity ratio of the magnetic-to-electric responses so far is 0.28.
Here, we propose an all-dielectric metafluid composed of crystalline
silicon nanospheres. First, we address the advantages of silicon as
a constituent material of a metafluid among major dielectrics. Next,
we experimentally demonstrate for the first time that a silicon nanosphere
metafluid exhibits strong electric and magnetic dipolar Mie responses
across the visible to near-infrared spectral range. The intensity
ratio of the magnetic-to-electric responses reaches unity. Finally,
we discuss the perspective to achieve unnaturally high (>3), low,
and even near-zero (<1) refractive index in the metafluid.