  Metasurfaces are ultrathin nanostructured surfaces that can allow arbitrary
manipulation of light. Implementing dynamic tunability into their design could
allow the optical functions of metasurfaces to be rapidly modified at will. The
most pronounced and robust tunability of optical properties is provided by
phase-change materials such as vanadium dioxide (VO2) and germanium antimony
telluride (GST), but their implementations have been limited only to
near-infrared wavelengths. Here, we demonstrate that VO2 nanoantennas with
widely tunable Mie resonances can be utilized for designing tunable
metasurfaces in the visible range. In contrast to the dielectric-metallic phase
transition-induced tunability in previous demonstrations, we show that
dielectric Mie resonances in VO2 nanoantennas offer remarkable scattering and
extinction modulation depths (5-8 dB and 1-3 dB, respectively) for tunability
in the visible. Moreover, these strong resonances are optically switchable
using a continuous-wave laser. Our results establish VO2 nanostructures as
low-loss building blocks of optically tunable metasurfaces.
