Memory loss and Auger processes in a many-body theory of charge transfer.

Charge transfer between hyperthermal alkali atoms and metallic scattering surfaces is an experimental and theoretical arena for many-body interactions. To model new facets, we use a generalized time-dependent Newns-Anderson Hamiltonian that includes electron spin, multiple atomic orbitals with image shifted levels, intra-atomic Coulomb repulsion, and resonant exchange. A variational electronic many-body wave function solves the dynamical problem. The wave function consists of sectors with zero and one particle-hole pair and goes beyond earlier work with the inclusion of amplitudes for a neutral atom plus an electron-hole pair. Higher-order sectors with more than one particle-hole pair are suppressed by powers of 1/N; hence the wave-function ansatz is equivalent to a 1/N expansion. The equations of motion are integrated numerically without further approximation. This solution shows improved loss of memory — the final charge state is independent of the initial one — in agreement with theoretical and experimental expectations. Understanding of this phenomenon is deepened through an analysis of entropy production. By studying the independentparticle approximation, and by examining the role played by different sectors of the Hilbert space in entropy production, we arrive at necessary and sufficient conditions for loss of memory to occur in the many-body solution. As further tests of the theory, we reproduce the experimentally observed peak in the excited neutral Li(2p) occupancy at intermediate work functions starting from different initial conditions. Next, we include Auger processes by adding two-body interaction terms to the many-body Hamiltonian. Several types of Auger processes are considered, and these are shown to affect the final-state occupancies at low work functions because phase space enlarges rapidly as the work function is lowered. Preliminary experimental evidence for an upturn in the Li(2p) occupancy at the lowest work functions thus may be explained by Auger transitions. Finally, we comment on the plausibility of observing a signature of the Kondo resonance in charge transfer experiments. @S0163-1829~96!01620-6#