engleski

Scattering of image potential band electrons by adatoms: A controlable decoherence mechanism in 2PPE from surfaces

The mechanisms of electron decoherence at surfaces are manifold as they may origi- nate from a variety of interactions of electrons with the static crystal structure and dynamical degrees of freedom of the environment. Typical examples of such mechanisms are the interactions with crystal inhomogeneities and defects, charge and spin density fluctuations, phonons, etc. Hence, the decoherence effects manifest themselves in spectroscopic data in a convoluted fashion and it is usually hard or even impossible to fully disentangle them from each other and deduce the targeted information because of the lack of control of underlying mechanisms by the external observer. However, hot electron propagation in quasi-two-dimensional image potential bands (IS-bands) on flat low index surfaces of some metals lends itself to the studies of a specific decoherence mechanism that can be controlled externally by a careful prepa- ration of the surface. By deliberately adding randomly distributed adsorbed atoms (scattering centers) on clean surfaces one can tune the strength of incoherent IS-electron scattering from adsorbates by varying their surface concentration (i.e. the coverage). Such scattering processes in IS-bands on Cu(100) surface have been investigated by two-photon-photoemission (2PPE) spectroscopy [1, 2] and interpreted using a simple Fermi golden rule (FGR) approach to calculation of the quasiparticle decay rates and scattering cross sections[2]. However, these results could reproduce the experimental data only in a limited IS-electron energy interval. Here we present a more elaborate theoretical description of electron decoherence in surface bands based on the propagator formalism[3] and infra-red renormalization of the quasiparticle self- energies. We demonstrate that by using this approach one can obtain a very good agreement between the calculated and measured values for the scattering cross sections over a wide interval of electron energies. This enables us to discuss different temporal stages of quasiparticle propagation and decoherence in surface bands that govern the intermediate step of 2PPE from surfaces.

Surface electronic bands; Electron scattering from adsorbates; Electron decoherence; Two-photon photoemission

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