Terahertz conductivity of the metal-insulator transition in a nanogranular VO2 film

Terahertz time-domain spectroscopy is used to measure the complex terahertz conductivity of a nanogranular vanadium dioxide (VO2) thin film as a function of temperature through the metal-insulator transition. The Drude–Smith model provides a good fit to the observed terahertz conductivity, revealing a metallic state that forms via switching of individual nanograins and strong carrier confinement within the nanograins due to scattering off grain boundaries. Furthermore, the directly applied Drude–Smith model provides a more accurate description of the measured terahertz conductivity in this material than either Bruggeman or Maxwell–Garnett effective medium theories.