Tracking the dynamics of the light-induced insulator-metal phase transition in VO₂ on atomic and nanoscopic length scales

Ultrafast control of material properties is an emerging route to engineer new properties transiently. However, there is still much to learn. While ultrafast techniques can have exceptional time resolution, they typically do so at the expense of spatial information, with most probes measuring average quantities over large areas. This loss of information can make understanding phase transitions particularly challenging as they may be heterogenous, making it difficult to know if defects or other local structures are dominating the response.

In this talk, I will summaries our approach to use X-ray Free Electron Lasers which enables us to see beyond the spatially averaged measurements at the atomic scale and nanoscale. I will show how diffuse X-ray scattering can be used to track how the distribution of the vanadium ion’s positions changes on the ultrafast timescale, which reveals that an ultrafast disordering processes drives the change in the long-range structural order on the femtosecond timescale [1].

In addition, I will show how soft X-ray coherent hyperspectral imaging can be used to track heterogeneity in the phase transition on a 25 nm length scale. Our methodology not only allows us to observe domain dynamics with a 150 fs time resolution, but allows to spectroscopically probe the electronic properties of the light induced domains [2].

Our results demonstrate the unexpected role of disorder and heterogeneity in ultrafast phase transitions