engleski

Extreme ultrafast dynamics of quasiparticles excited in surface electronic bands

Recent developments of energy and time resolved photoelectron spectroscopies have enabled the measurements of surface electronic processes in the real time domain. Experiments in which the time scales of relaxation are much shorter than the duration of measurement provide information on asymptotic steady state dynamics of the excited system. Descriptions of the steady state electron dynamics at surfaces are commonly given in terms of the rate constants that characterize asymptotic energy relaxation and decay of quasiparticle states. However, if the act of measurement proceeds on the time scale comparable to or shorter than the relaxation processes caused by the intermediate or final state interactions in the system the thus probed quasiparticle evolution may considerably differ from the asymptotic behaviour described by the rate constants. Hence, reliable interpretations of the measurements in the extreme ultrafast regime should be based on nonasymptotic descriptions of the evolution of the excited system. In this work we develop a many-body description of nonadiabatic uasiparticle dynamics in surface bands valid on the extreme ultrashort time scale by combining the formalism for calculation of quasiparticle survival probabilities with the selfconsistent treatment of the substrate electronic response. Applying this approach to the benchmark Cu(111) surface we assess the behavior and intervals of preasymptotic quasiparticle dynamics in quasi-two-dimensional surface bands and identify the transitions to asymptotic regime of exponential decay characterized by the Fermi golden rule type of transition rate. The general validity of these findings enables drawing distinctions among the various regimes of ultrafast electron dynamics that may be revealed by modern time resolved spectroscopies.

surface electronic bands; ultrafast dynamics; decay; decoherence

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