Probing the structural evolution across the metal-to-insulator transition in thin film VO2 using nonlinear optics*

Time-resolved pump-probe studies on VO2 have demonstrated that a phase transition in both the electronic and structural degrees of freedom can be induced using sub-picosecond light pulses. However, typically the electronic and structural degrees of freedom are separately measured using time-resolved optical and diffraction based techniques respectively. Therefore the timescales of electronic and structural dynamics are typically compared across different samples and different experimental setups. Here we introduce the use of rotational anisotropy nonlinear optical generation spectroscopy as a method to probe the structural symmetry of VO2 purely optically. We demonstrate that the low temperature monoclinic and high temperature rutile phases in a VO2 thin film grown on r-cut sapphire (1-102) are clearly resolved using our technique and compared favorably with calculations. We will discuss how a simultaneous probe of ultrafast electronic and structural dynamics in VO2 can be realized using this technique.