Thermal hysteresis in scattering by vanadium-dioxide spheres

Abstract

Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal on being heated from 58 • C to 72 • C, the transformation being reversible but hysteretic. Electromagnetically, VO2 transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength λ0 < 1100 nm, but from a dissipative dielectric to a plasmonic metal (or vice versa) if λ0 > 1100 nm. Calculating the extinction, total scattering, absorption, radiation-pressure, back-scattering, and forward-scattering efficiencies of a VO2 sphere, we found clear signatures of thermal hysteresis in (i) the forward-scattering, back-scattering, 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.