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

Abstract

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 a as a function of temperature. We employ quantum-kinetic equations for the projectile Green functions in the finite-U noncrossing approximation. Our results for a 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 a. The experimentally found nonmonotonous temperature dependence, however, could not be reproduced. Instead of an initially increasing and then decreasing a, 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.

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.…”

Electron kinetics at the plasma interface

“…Second, the selfenergies are calculated in the non-crossing approximation and, third, the fact is utilized that the selfenergies are peaked around the time-diagonal enabling a saddle-point approximation to extract from the Dyson equations rate equations for the occurrence probabilities n i (t), n t (t), n s (t), and n g (t) for, respectively, the ion, the two metastable states, and the groundstate of the projectile. Following this reasoning which we also exerted in [36,38,39] we get…”

“…Besides the well-known twoelectron Auger processes (Ref. [55] and below) we investigated secondary electron emission due to auto-detaching negative ions [36,37] and analyzed resonant neutralization of ions with an eye on mixed-valence and Kondo resonances [38,39]. Our work on electron extraction from surfaces due to impacting atomic particles is based on multi-channel Anderson-Newns models [56] parameterized by experimental energies and target-projectile interactions deduced from considerations based on image charges [57,58].…”

“…The energies ε g (t), ε * s (t), ε * t (t), and ε qσ (t) of the projectile's electronic configurations are time-dependent because of polarization effects which depend on the projectile's distance to the surface and thus its instantaneous position in front of the surface. We approximate this by an image shift as explained in [37,39]. The time-dependencies of the matrix elements V SET kσ (t) for single electron transfer, V AN k1k2k σ↓ (t) for Auger neutralization, V DAD kk σ (t) for direct Auger de-excitation, and V IAD kqσ (t) for indirect Auger deexcitation arise from the overlap of projectile and target wave functions which also depend on the separation of the projectile and the target.…”

Towards an integrated modeling of the plasma-solid interface

“…This concerns the neutralization of low-energy ions, e.g. [210] and their stopping in the solid, as well as the electron dynamics across the interface, e.g. [20].…”