Thermal hysteresis in scattering by VO₂ spheres

Vanadium dioxide (VO₂) transforms from purely monoclinic to purely tetragonal when heated from 58^◦C to 72^◦C, and the transformation is reversible but hysteretic. Electromagnetically, VO₂ transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength is λ₀ < 1100 nm; it transforms from a dissipative dielectric to a plasmonic metal (or vice versa) if λ₀ > 1100 nm. Calculating the extinction, total scattering, absorption, radiation pressure, backscattering and forward-scattering efficiencies of a VO₂ sphere, we found clear signatures of thermal hysteresis in (i) the forward-scattering, backscattering, and absorption efficiencies for λ₀ < 1100 nm, and (ii) the forward-scattering, backscattering, total scattering, and absorption efficiencies for λ₀ > 1100 nm. Vacuum and null-permittivity quasistates occur between 58^◦C and 72^◦C, when tetragonal VO₂ is a plasmonic metal, once each on the heating branch and once each on the cooling branch of thermal hysteresis. But none of the six efficiencies show significant differences between the two quasistates.