Berlin 2012 – scientific programme
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O: Fachverband Oberflächenphysik
O 12: Surface dynamics
O 12.13: Talk
Monday, March 26, 2012, 19:00–19:15, H 2013
Excitonic features in image-potential resonances on Si(100) probed by two-photon photoemission — •Martin Weinelt1,2, Christian Eickhoff1,2, and Cornelius Gahl1,2 — 1Max-Born-Institut, Max-Born-Straße 2a, 12489 Berlin, Germany — 2Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
Electronic transitions into unoccupied image-potential resonances n=1 and n=2 on silicon(100) were studied with angle-resolved femtosecond pump-probe photoelectron spectroscopy. Off-resonant excitation out of valence bands unveils the typical behavior of electrons trapped in the image-potential in front of a surface, characterized by a well-defined binding energy [1] and an effective mass of 1. However, tuning the excitation energy of the pump-pulse across the resonance between the occupied dangling-bond Dup and unoccupied n=1,2 surface states reveals excitonic features, both in the dispersion and the binding energy of the probed state. As photoemission probes the population of specific states, resonant excitation out of the discrete Dup surface state implies the formation of a surface exciton population on a femtosecond timescale.
[1] P. M. Echenique and J. B. Pendry, J. Phys. C 11, 2065 (1978)