Memory Loss and Auger Processes in a Many Body Theory of Charge Transfer

TL;DR

This paper develops a many-body theoretical model for charge transfer between alkali atoms and metal surfaces, incorporating complex interactions and Auger processes, and demonstrates improved understanding of memory loss and experimental phenomena.

Contribution

It introduces a generalized time-dependent Hamiltonian with a variational wave function including multiple sectors, and analyzes entropy production and Auger effects in charge transfer.

Findings

Final charge states become independent of initial conditions, showing loss-of-memory.

Reproduces experimental peak in neutral Li(2p) occupancy at intermediate work functions.

Auger processes influence final state occupancies at low energies.

Abstract

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 which 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 either zero or one particle-hole pair and goes beyond earlier work through 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. The 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 independent-particle 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