Energy transfer between electrons and ions in dense displacement cascades

A theory of the energy exchange between valence electrons and ions in the dense displacement cascades in metals is proposed. It is shown that the theory based on the relaxation of the nonequilibrium electron-ion system gives a common basis for the electronic stopping power of slow ions due to valence electrons and for the energy transfer via an electron-phonon interaction. It is found that the energy loss owing to the electron-phonon interaction bears a close relationship to the electronic stopping power, but it is greatly enhanced because of the emergence of phonon excitations and band structure. The corresponding cooling rates of the thermalizing cascade are several times greater in metals with a strong electron-ion interaction than in metals with a weak interaction. A similar conclusion holds in the intermediate region, where the ions in the thermalizing cascade are essentially free to move but band-structure effects persist. However, conduction electrons play a role in the cooling of the cascade only if the dynamics of the ions gives rise to phonons.