Correlated electron effects in low energy alkaline earth ion scattering

The spin correlations of many electrons can lead to emergent phenomena that cannot be extrapolated from the behavior of independent electrons. The role of such multi-electron processes in charge exchange during atom-surface collisions remains a challenging and unsolved problem. Two prior independent theoretical investigations predicted that when a projectile has a single unpaired electron or hole, this localized spin impurity would induce a Kondo resonance at the Fermi energy leading to a mixed-valent state in the metal conduction band. The occupancy of this sharp state would be a strong function of the surface temperature, which would cause an anomalous temperature dependence of the neutralization probability in a scattering experiment. We demonstrate such dependence for low energy Sr$^{+}$ scattered from clean polycrystalline gold. This unusual temperature dependence is amplified when the metal work function is reduced by embedding Sr atoms into the material.