Many-body theory of charge transfer in hyperthermal atomic scattering

Abstract

We use the Newns-Anderson Hamiltonian to describe many-body electronic processes that occur when hyperthermal alkali atoms scatter off metallic surfaces.Following Brako and Newns, we expand the electronic many-body wavefunction in the number of particle-hole pairs (we keep terms up to and including a single particle-hole pair). We extend their earlier work by including level crossings, excited neutrals and negative ions. The full set of equations of motion are integrated numerically, without further approximations, to obtain the many-body amplitudes as a function of time. The velocity and work-function dependence of final state quantities such as the distribution of ion charges and excited atomic occupancies are compared with experiment. In particular, experiments that scatter alkali ions off clean Cu(001) surfaces in the energy range 5 to 1600 eV constrain the theory quantitatively. The neutralization probability of Na + ions shows a minimum at intermediate velocity in agreement with the theory. This behavior contrasts with that of K + , which shows virtually no neutralization, and with Li + , which exhibits a monotonically increasing neutral fraction with decreasing velocity. Particle-hole excitations are left behind in the metal during a fraction of the collision events; this dissipated energy is predicted to be quite small (on the order of tenths of an electron volt). Indeed, classical trajectory simulations of the surface dynamics account well for the observed energy loss, and thus provide some justification for our truncation of the equations of motion at the single particle-hole pair level. Li + scattering experiments off low work-function surfaces provide qualitative information on the importance of many-body effects. At sufficiently low work function, the negative ions predicted to occur are in fact observed. Excited neutral Li atoms (observed via the optical 2p → 2s transition) also emerge from the collision. A peak in the calculated Li(2p) → Li(2s) photon intensity occurs at intermediate work function in accordance with measurements.

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

“…It was first applied to the dynamical problem in 1985 by Brako and Newns 23 ; three sectors were included in this pioneering work. Subsequent work work extended this ansatz 24,16,15 . The improved ansatz for our wavefunction now has six sectors (for details, see [I]):…”

Internal electronic structure of adatoms on Fe(110) and Fe(100) surfaces: A low-energyLi+scattering study

“…͑1͒ for the analysis of our data by comparing, in certain instances, the N obtained from Eq. ͑1͒ to the N obtained by a complete solution of the Newns-Anderson Hamiltonian in the independent particle picture 15,42,43 and found them to be comparable.…”

“…42,43 Typically, the charge formation process is described by the energy and virtual width of the valence level of the scattered projectile, and the time dependence of the level energy and width produces nonadiabatic excitations in the atom-surface system. While the energy of the valence level is mostly governed by the surface electrostatic potential, the width of the valence level is determined by electron exchange between the atom and the metal surface.…”

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

“…(24) has been defined in the literature in two ways. The random phase approximation (RPA) exactly follows the derivation above and consequently R is the Fourier-transformed Coulomb potential [109,110] …”

“…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].…”