Thermal hysteresis in scattering by VO₂ spheres

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optics

Background:

• Vanadium dioxide (VO2) undergoes a reversible phase transition from monoclinic to tetragonal between 58°C and 72°C.
• This transition alters VO2's electromagnetic properties, transitioning between dielectric and plasmonic metallic states depending on the free-space wavelength (λ0).

Purpose of the Study:

• To investigate the signatures of thermal hysteresis in the optical efficiencies of a VO2 sphere.
• To analyze the electromagnetic behavior of VO2, specifically its dielectric and plasmonic metallic states.

Main Methods:

• Calculation of extinction, total scattering, absorption, radiation pressure, backscattering, and forward-scattering efficiencies for a VO2 sphere.
• Analysis of these efficiencies across different free-space wavelengths (λ0 < 1100 nm and λ0 > 1100 nm) and temperatures.

Main Results:

• Clear signatures of thermal hysteresis were observed in forward-scattering, backscattering, and absorption efficiencies for λ0 < 1100 nm.
• For λ0 > 1100 nm, hysteresis was evident in forward-scattering, backscattering, total scattering, and absorption efficiencies.
• Vacuum and null-permittivity quasistates were identified during the heating and cooling cycles, where tetragonal VO2 behaves as a plasmonic metal.

Conclusions:

• The study confirms thermal hysteresis in VO2's optical response, with distinct signatures depending on the wavelength.
• The findings highlight the potential of VO2 for applications leveraging its tunable dielectric and plasmonic properties.