Lifetime of excited electronic states at surfaces: Comparison between the alkali/Cu(111) systems

Abstract

Time-resolved two-photon photoemission of alkali adsorbates on noble-metal surfaces revealed the existence of very long-lived excited electronic states. The present work is devoted to the study of the lifetime of electronically excited states in the alkali/Cu(111) systems. The cases of Na, K, Rb, and Cs are investigated. The decay by one-electron transitions (resonant charge transfer) and by multielectron interactions (inelastic electron-electron scattering in the bulk and at surface) is evaluated in a joint wave-packet propagation and many-body metal response approach. The origin of the stabilization of the excited states is stressed and the difference between the decay rates of the various alkalis is discussed and shown to be connected to the alkali polarizability. The present theoretical results are compared with the available experimental data.