Measuring correlated-electron effects with low energy alkaline earth ion scattering

A system of many electrons can display emergent phenomena beyond what would be predicted from the behavior of individual electrons. A method for triggering correlated electron behavior is to introduce a spin impurity into a metal, which causes the free electrons to respond collectively. In the present work, the unpaired valence electron on singly charged alkaline earth ions is used to provide the spin impurity during low energy ion scattering experiments. Previous calculations have suggested that electron correlations would result in an anomalous temperature dependence of the ion neutralization probability. The neutralization of magnesium (Mg) scattered from polycrystalline gold (Au) shows little dependence on temperature. Scattered strontium (Sr) does, however, show a marked temperature dependence of the neutralization that provides clear evidence of electron correlations. The results are discussed in terms of the velocity of the outgoing projectiles.