Imaging ultrafast electronic domain fluctuations with X-ray speckle visibility

TL;DR

This paper demonstrates a novel X-ray speckle visibility technique at an X-ray free-electron laser to observe ultrafast electronic domain fluctuations in a quantum material, revealing liquid-like charge dynamics.

Contribution

It introduces a split-and-delay setup for nonequilibrium speckle experiments, enabling detection of ultrafast local structural changes in materials under optical stimuli.

Findings

Electronic domain fluctuations exhibit liquid-like behavior.

Ultrafast charge dynamics differ from thermal processes.

Demonstrated method captures nonequilibrium nanoscale dynamics.

Abstract

Speckle patterns manifesting from the interaction of coherent X-rays with matter offer a glimpse into the dynamics of nanoscale domains that underpin many emergent phenomena in quantum materials. While the dynamics of the average structure can be followed with time-resolved X-ray diffraction, the ultrafast evolution of local structures in nonequilibrium conditions have thus far eluded detection due to experimental limitations, such as insufficient X-ray coherent flux. Here we demonstrate a nonequilibrium speckle visibility experiment using a split-and-delay setup at an X-ray free-electron laser. Photoinduced electronic domain fluctuations of the magnetic model material Fe$_{3}$O$_{4}$ reveal changes of the trimeron network configuration due to charge dynamics that exhibit liquid-like fluctuations, analogous to a supercooled liquid phase. This suggests that ultrafast dynamics of electronic heterogeneities under optical stimuli are fundamentally different from thermally-driven ones.