Imaging Ultrafast Phase Transitions in Quantum Materials

Phase transitions are heterogenous phenomena that we experience every day. If we watch a pot boil as we heat it, we see gas bubbles form in specific places and they grow in size as the water gets hotter and over a certain range the water can coexist in both liquid and gas phases. Over the last few decades, we have shown that there is an alternative route to driving phase transitions, not with heat, but with light. By using ultra-short pulses of light, we can drive phase transitions on femtosecond timescales and in some cases access phases that are not accessible to heat alone. The question we seek to address is, do these type of non-equilibrium phase transitions follow the same pathway as our boiling water? Are they heterogenous? or does some other mechanism come into play?

This question has been difficult to answer, because while we have probes that can produce static images with exceptional spatial resolution, or capture dynamics with exquisit temporal resolution, we have not had probes that can do both at the same time! In this talk, I will show how using coherent X-rays from an X-ray Free Electron Laser can achieve both simultaneously, and I will present our first works on imaging ultrafast, light-driven phase transitions at the nanoscale.