Probing Electronic Fluxes via Time-Resolved X-Ray Scattering

The current flux density is a vector field that can be used to describe theoretically how electrons flow in a system out of equilibrium. In this work, we unequivocally demonstrate that the signal obtained from time-resolved x-ray scattering does not only map the time evolution of the electronic charge distribution, but also encodes information about the associated electronic current flux density. We show how the electronic current flux density qualitatively maps the distribution of electronic momenta and reveals the underlying mechanism of ultrafast charge migration processes, while also providing quantitative information about the timescales of electronic coherences.