Nonthermal acceleration of atoms as a mechanism of fast lattice heating in ion tracks

Abstract

Atomic heating in a solid takes place after an impact of a swift heavy ion within a time of electronic cooling there, i.e., ∼100 fs. This implies an extremely fast electron–ion energy exchange (“electron–phonon coupling”) necessary for the production of detected ion tracks. In contrast, laser irradiation experiments and calculations show too slow electron–phonon energy exchange to cause structural changes detected in swift heavy ion tracks in solids. We demonstrate that this contradiction can be resolved by taking into account that electron–phonon coupling is not the sole mechanism of energy exchange between electrons and ions in condensed matter. Excitation of the electronic system alters the potential energy surface of atoms, causing them to accelerate and increase their kinetic energy at ultrashort times.