Room-temperature Kondo effect in atom-surface scattering: Dynamical1/Napproach

Abstract

The Kondo effect may be observable in some atom-surface scattering experiments, in particular, those involving alkaline-earth atoms. By combining Keldysh techniques with the NCA approximation to solve the time-dependent Newns-Anderson Hamiltonian in the U → ∞ limit, Shao, Nordlander, and Langreth found an anomalously strong surface-temperature dependence of the outgoing charge state fractions. Here we employ a dynamical 1/N expansion with a finite Coulomb interaction U to give a more realistic description of the scattering process. We test the accuracy of the 1/N expansion in the N = 1 case of spinless fermions against the exact independent particle solution. We then compare results obtained in the U → ∞ limit with the NCA approximation at N = 4 and recover qualitative features already found. Finally, we analyze the realistic situation of Ca atoms with U = 5.8 eV scattered off Cu(001) surfaces. Although the presence of the doubly-ionized Ca ++ species can change the absolute scattered Ca + yields, the temperature dependence is qualitatively the same as that found in the U → ∞ limit. One of the main difficulties that experimentalists face in attempting to detect this effect is that the atomic velocity must be kept small enough to limit kinematic smearing of the Fermi surface of the metal.

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

“…A Kondo resonance near the Fermi energy is induced by the single valence electron on the projectile [3], as illustrated in Fig. 1B.…”

“…40 Ca + was the species modeled in the calculations of Ref. [3], and would ordinarily have been the natural species to use because the match between ionization energy and surface work function should lead to easily measurable changes in the neutralization probability with temperature. The difficulty we encountered with Ca, however, was in obtaining a pure beam.…”

“…Shao et al [2] and Merino and Marston [3] had independently predicted that when a projectile ion has a single unpaired electron or hole, correlated electron behavior would induce either a Kondo resonance or mixed-valent state at the Fermi energy. The particular resonance formed would be a function of the projectile-surface distance, but the occupancy of the state and the subsequent neutralization rate in a scattering experiment would be a strong function of the surface temperature.…”

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.…”

Auger neutralization and ionization processes for charge exchange between slow noble gas atoms and solid surfaces

“…1). Resonant processes, being one-electron ones, have been described abundantly in the literature, practically for any atom/solid combination, using different techniques [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38].…”