  Subwavelength nanoparticles can support electromagnetic resonances with
distinct features depending on their size, shape and nature. For example,
electric and magnetic Mie resonances occur in dielectric particles, while
plasmonic resonances appear in metals. Here, we experimentally demonstrate that
the multipolar resonances hosted by VO2 nanocrystals can be dynamically tuned
and switched thanks to the insulator-to-metal transition of VO2. Using both Mie
theory and Maxwell Garnett effective medium theory, we retrieve the complex
refractive index of the effective medium composed of a slab of VO2 nanospheres
embedded in SiO2 and show that such a resulting metamaterial presents distinct
optical tunability compared to unpatterned VO2. We further show that this
provides a new degree of freedom to design low-loss phase-change metamaterials
with designer optical tunability and actively controlled light scattering.
