Paper SS2-WeM4
Multi-Electron Effects in Low Energy Sr⁺ Ion Scattering

Wednesday, October 20, 2010, 9:00 am, Room Santa Ana

A system of many electrons can display emergent phenomena that cannot be extrapolated from the behavior of independent electrons. Non-adiabatic resonant charge transfer is used to reveal this multi-electron behavior by employing singly charged alkaline earth ions in a low energy ion scattering experiment. The spin of the single valence electron of such an ion behaves as a magnetic impurity that interacts with the continuum of many-body excitations in the metal, resulting in Kondo and mixed valence resonances near the Fermi energy.^1,2 The occupation of these resonances is acutely sensitive to changes of surface temperature, which leads to an anomalous temperature dependence of the ion neutralization properbility. We report a maximum in the neutralization probability near 600 K for 2-4 keV Sr⁺ ions scattered from polycrystalline gold. Correlated electron effects, which have traditionally been manifest at low temperature, are observable well above room temperature because the projectile’s ionization level shifts and crosses the target’s Fermi energy as it approaches the surface where the interaction between the localized and extended electrons is very strong. This interaction becomes more pronounced as the work function of the surface is lowered by Sr implantation into the near-surface region. Further study will involve well-characterized single crystal surfaces that will enable detailed investigation of the relationships between the formation of correlated electron states and the atomic structure of the solid.

¹H. X. Shao, P. Nordlander, and D. C. Langreth, Phys. Rev. Lett. 77, 948 (1996).

²J. Merino and J. B. Marston, Phys. Rev. B 58, 6982 (1998).