Correlated Electron Effects in Low EnergySr+Ion Scattering

Abstract

Resonant charge transfer during low energy ion scattering reveals correlated-electron behavior at high temperature. The valence electron of a singly charged alkaline-earth ion is a magnetic impurity that interacts with the continuum of many-body excitations in the metal, leading to Kondo and mixed valence resonances near the Fermi energy. The occupation of these resonances is acutely sensitive to the surface temperature, which results in a marked temperature dependence of the ion neutralization. We report such a dependence for low energy Sr(+) scattered from polycrystalline gold.

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

“…4 shows the temperature dependence of the NF for 2.0 keV Sr + ions scattered from clean polycrystalline Au. The NF rises with temperature until it reaches a maximum at around 600 K, above which it drops [12]. In Ref.…”

“…In Ref. [12], we were able to rule out any structural or compositional changes with temperature that could have been responsible for this behavior. Instead, the maximum was attributed to two competing processes.…”

“…The increase in NF prior to 600 K is assigned to the rise associated with the enhancement in the population of states just above the Fermi energy with temperature [11]. When the temperature passes 600 K, the electrons reach the mixed-valent state induced by electron correlations whose population have a negative temperature dependence [12].…”

“…In a recent letter, we reported measurements of the neutralization of scattered strontium ions (Sr + ) from polycrystalline gold (Au) as a function of surface temperature [12]. These data showed that the NF first increased to a maximum at around 600 K, and then decreased.…”

Time Evolution of the Kondo Resonance in Response to a Quench

“…This contrasts with their equilibrium properties, which are largely well understood [1], or can be investigated within a number of highly accurate methods, such as the numerical renormalization group method (NRG) [2][3][4][5], the continuous time quantum Monte Carlo (CTQMC) approach [6], the density matrix renormalization group [7], or the Bethe ansatz method [8,9]. Quantum impurity models far from equilibrium are of direct relevance to several fields of research, including charge transfer effects in lowenergy ion-surface scattering [10][11][12][13][14][15][16][17], transient and steady state effects in molecular and semiconductor quantum dots [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36], and also in the context of dynamical mean field theory (DMFT) of strongly correlated lattice models [37][38][39], as generalized to nonequilibrium [40][41][42]. In the latter, further progress hinges on an accurate non-perturbative solution for the nonequilibrium Green functions of an effective quantum impurity model.…”