Absence of hysteresis in n-k space during the phase transition of vanadium dioxide

Abstract

Thermal hysteresis in the optical and electrical properties of VO2 when cycling the temperature through insulator-to-metal states is well known. Here we show that no hysteresis is observed in the co-evolution of the real and imaginary parts of the refractive index, or equivalently, in the evolution of the polarization state of light reflected from a film. Using models for the effective optical properties of inhomogeneous materials, we show that this observation is consistent with a two-phase composition having similar depolarization factors during the temperature cycling. Absence of hysteresis also rules out the possibility of light acquiring different polarization states when interacting with the material during a full cycle of the phase transition. Such considerations are important to understand the functioning of VO2-based photonic devices.