Many-body theory of the neutralization of strontium ions on gold surfaces

Motivated by experimental evidence for mixed-valence correlations affecting the neutralization of strontium ions on gold surfaces we set up an Anderson-Newns model for the Sr:Au system and calculate the neutralization probability $\alpha$ as a function of temperature. We employ quantum-kinetic equations for the projectile Green functions in the finite$-U$ non-crossing approximation. Our results for $\alpha$ agree reasonably well with the experimental data as far as the overall order of magnitude is concerned showing in particular the correlation-induced enhancement of $\alpha$. The experimentally found non-monotonous temperature dependence, however, could not be reproduced. Instead of an initially increasing and then decreasing $\alpha$ we find over the whole temperature range only a weak negative temperature dependence. It arises however clearly from a mixed-valence resonance in the projectile's spectral density and thus supports qualitatively the interpretation of the experimental data in terms of a mixed-valence scenario.