Phase changes are central to the world around us. Probably the most familiar example is when ice melts into water or water boils into steam, but phase changes also underlie heating systems and even digital memory, such as that used in smartphones.

Triggered by pulses of light or electricity, some materials can switch between two different phases that represent binary code 0s and 1s to store information. Understanding how a material transforms from one state or phase to another is key to tailoring materials with specific properties that could, for instance, increase switching speed or operate at lower energy costs.

Yet researchers have never been able to directly visualize how these transformations unfold in real time. We often assume materials are perfect and look the same everywhere, but “part of the challenge is that these processes are often heterogeneous, where different parts of the material change in different ways, and involve many different length scales and timescales,” said Aaron Lindenberg, co-author and SLAC and Stanford University professor.