Extreme Ultrafast Dynamics of Quasiparticles Excited in Surface Electronic Bands

Abstract

We develop a many-body description of the nonadiabatic dynamics of quasiparticles in surface bands valid on an extremely ultrashort time scale by combining the formalism for the calculation of quasiparticle survival probabilities with the self-consistent treatment of the electronic response of the system. Applying this approach to the benchmark Cu(111) surface, we assess the behavior and intervals of preasymptotic electron and hole dynamics in surface bands and locate the transition to the asymptotic regime of the exponential quasiparticle decay characterized by the corrected Fermi golden rule-type of transition rate. The general validity of these findings enables distinguishing the various regimes of ultrafast electron dynamics that may be revealed in time resolved experiments. DOI: 10.1103/PhysRevLett.97.086801 PACS numbers: 73.20.ÿr, 71.10.ÿw, 78.47.+p, 79.60.ÿi The development of time resolved electron spectroscopies has enabled measurements of the surface electronic processes in the real time domain [1][2][3][4][5]. Such experiments provide direct insight into the temporal evolution of the studied systems from which information on the various relaxation processes that govern the dynamics of excited quasiparticles can be deduced. Experiments in which the time scales of relaxation are much shorter than the duration of measurement provide information on the asymptotic steady state dynamics of the excited system in its passage towards thermodynamic equilibrium. Descriptions of these processes are commonly given in terms of the rate constants that characterize asymptotic relaxation of quasiparticle states.Methods for probing the dynamics of electronic states in confined systems are usually based on electron excitation from or injection into the system, either in the one-step processes, as in direct photoemission (PE) or inverse photoemission (IPE) spectroscopy, or in the two-step laser pump-probe induced transitions, as in two-photon photoemission (2PPE) experiments. Common to all these experiments is a sudden promotion of electrons (holes) in the initially unoccupied (occupied) states after which their motion is subjected to final state (PE and IPE) or intermediate state interactions (2PPE) with the remainder of the system. These interactions give rise to relaxation and decoherence of the excited quasiparticles [6] and produce effects in the measured spectra from which the dynamics of the excited system is assessed. Energies and lifetimes of quasiparticles in surface bands have been experimentally determined dominantly in the regimes of separated time scales of relaxation and measurement and interpreted in the framework of asymptotic decay of excited states [5].However, if the act of measurement proceeds on the time scale comparable to or shorter than that of relaxation and decoherence processes, as in recent employments of laser pulse spectroscopies [7] or novel applications of x-ray techniques [8] with extreme temporal precision, the thus probed quasiparticle evolution may considerably differ from asympto...

The influence of electron confinement, quantum size effects, and film morphology on the dispersion and the damping of plasmonic modes in Ag and Au thin films

“…[100]. been demonstrated to be dispersive [363,364]. Hence, the s-like SP overlaps in a broad range in energy-momentum space with the e-h continuum.…”

Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination

“…The mechanism that we propose is the following: electrons excited in the bulk that are being extracted through the surface layers would pass through few atomic layers with smooth and gapless connection to the higher-density surface states shown in figure 10 and would thermalize quickly into those surface states. We expect thermalization to be very rapid [64] because it occurs within a single band which terminates in surface states (intraband relaxation within the sulfur p-band). As such, dissipation is suggested to take place on the femtosecond scale [65]-even if excitations could occur in the bulk at a higher level, these electrons would not contribute to higher effective OCV.…”

Time-dependent electron phenomena at surfaces

“…For longer times, the key magnitude is the plasma frequency ω p , and a different scaling time 1∕ω p is found (26). These longer-time oscillations are relevant for the preasymptotic decay and dephasing of quasiparticles for some surface and image potential states (29).…”