  Highly energetic ions that impact materials have applications from
semiconductor industry to medicine, and are fundamentally interesting as they
trigger multi-length and time-scale processes. In particular, they excite
electrons into non-thermalized energy distributions with subsequent
non-equilibrium electron-electron and electron-ion dynamics. In order to
achieve a quantitative description of these, we propose a general
first-principles framework that bridges time scales from ultrafast electron
dynamics directly after impact, to ion diffusion over migration barriers in
semiconductors. We apply it to magnesium oxide under proton irradiation and
discover a diffusion mechanism that is mediated by hot electrons. Our
quantitative simulations show that this mechanism strongly depends on the
projectile-ion velocity. This indicates that it may occur only at a specific
penetration depth in the target and that it can be triggered by varying the
kinetic energy of the particle radiation. Either of these predictions should
facilitate direct experimental observation of this effect and significantly
advances current understanding of non-equilibrium electron-ion dynamics.
