Electron scattering by random adsorbates: A tunable decoherence mechanism in surface bands

Abstract

AbstractMechanisms of electron decoherence at surfaces are manifold as they may originate from the various complex interactions of electrons with the static crystal structure and dynamical degrees of freedom of the environment. Decoherence effects manifest themselves in the spectroscopic data in a convoluted fashion and it is usually hard or even impossible to fully disentangle them from each other because of the lack of control of underlying mechanisms by the external observer. However, electronic propagation in quasi‐two‐dimensional image potential bands (IS‐bands) on flat low index surfaces of some metals is subject to an efficient decoherence mechanism that can be controlled externally by careful preparation of the surface. By dosing the concentration (i.e. the coverage) of adsorbates on clean surfaces, which act as randomly distributed scattering centres, one can tune the strength of incoherent IS‐electron scattering from defects. Such processes in IS‐bands on Cu(100) surface have been investigated by two‐photon‐photoemission (2PPE) spectroscopy and interpreted using Fermi golden rule approach to calculation of the quasiparticle decay rates and scattering cross sections. However, these results could reproduce the experimental data only in a limited energy interval. Here, we employ the description of electron decoherence in IS‐bands based on the propagator approach and infrared renormalization of quasiparticle self‐energy and demonstrate that it gives a very good agreement between the theoretical and experimental results for the cross sections. This enables us to discuss the temporal stages of electron dynamics and decoherence in the intermediate states of 2PPE spectroscopy of surface bands.