  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.
