Multipolar resonances with designer tunability using VO₂ phase-change materials

Abstract

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 Si⁢O₂ and show that such a resulting metamaterial presents distinct optical tunability compared to unpatterned VO₂. We further show that this approach provides a new degree of freedom to design low-loss phase-change metamaterials with record large figure of merit (△n△k) and designer optical tunability.