[seminar] podsjetnik na DANASNJI seminar na IF-u u 15:00h

[Vlasta Horvatic]

Postovani,
podsjecamo Vas na danasnji seminar na 

Institutu za fiziku u 15:00 sati:



      Institut za fiziku, Bijenicka cesta 46,

      predavaonica u zgradi Mladen Paic

       

       

      u ponedjeljak, 19. prosinca 2011. u 15:00 sati
     
       

      Transient Excitons on Metals: Fact or Fiction?
     
      Prof. dr. Hrvoje Petek
     
      Department of Physics and Astronomy, University of Pittsburgh, USA

      E-mail: petek at pitt.edu 
     
       

      The high electron density within metals screens the Coulomb interaction efficiently on the length scale of interatomic distance and the time scale of inverse plasma frequency, i.e., typically in the sub-femtosecond regime.  Nevertheless, transient excitonic interactions have been invoked in theoretical descriptions of the renormalization of optical spectral density and hot electron lifetimes in noble metals.  We explore the surface electronic structure of silver and copper surfaces by energy, momentum, and time-resolved multiphoton photoemission.  Features observed in the near-resonant multi-photon photoemission spectra cannot be understood from the joint density of preexisting occupied and unoccupied states that are coupled by optical transitions and a Fermi Golden Rule transition rate formalism, suggesting that quasiparticle correlations, for example, transient excitonic interaction between photoexcited electron and hole, as well as delayed formation of image potential states may affect the transition amplitudes and quasiparticle lifetimes.  Different behavior observed for copper and silver surfaces suggest that the observed behavior may be a manifestation of inefficient Coulomb screening leading to transient excitonic interactions and the retarded formation of image potential states that have been predicted theoretically by Gumhalter and coworkers.

       

      http://www.physicsandastronomy.pitt.edu/people/hrvoje_petek
     
       

      Voditelji seminara IF-a: Vlasta Horvatic i Ivica Zivkovic
     
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