  Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal
on being heated from 58 deg C to 72 deg C, the transformation being reversible
but hysteretic. Electromagnetically, VO2 transforms from a dissipative
dielectric to another dissipative dielectric if the free-space wavelength is
less than 1100 nm, but from a dissipative dielectric to a plasmonic metal (or
vice versa) if the free-space wavelength exceeds 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 free-space wavelength less than 1100 nm, and (ii)
the forward-scattering, back-scattering, total scattering, and absorption
efficiencies for free-space wavelength more than 1100 nm. Vacuum and
null-permittivity quasistates occur between 58 deg C and 72 deg 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.

Optics