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O: Oberflächenphysik

O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)

O 15.72: Poster

Freitag, 4. März 2005, 17:00–20:00, Poster TU D

Electron-electron correlations at the LiF(100) surface probed via (e,2e) spectroscopy — •Frank O. Schumann, Jamal Berakdar, and Jürgen Kirschner — MPI f. Mikrostrukturphysik, Weinberg 2, 06120 Halle

Electronic correlations manifest themselves in many-body effects like superconductivity and magnetism. Due to the Coulomb and exchange interaction two electrons tend to avoid each other leading to an exchange-correlation hole. We studied the correlation between two electrons by probing the emission of electron pairs from a LiF(100) surface upon excitation with 32 eV primary electrons. The set-up consists of a channelplate, followed by a central collector and a pulsed electron gun. The energy of the electrons follows from their flight times. We find correlation in energy and k-space of an electron pair, where one electron originates from the top of the valence band. We selected the energies of the ejected electron pair to be E₁=9 eV and E₂=8 eV, respectively. Mapping the correlation as a function of the in-plane momentum of the second electron results in the observation of a zone of reduced intensity. The extension of this exchange-correlation hole is ∼1 Å⁻¹ which is in the range of theoretical predictions on double photoemission. Another experimental fact is the sensitivity of the correlation hole to decoherence effects, an aspect which is largely unexplored theoretically. Increasing the impinging electron energy to 33.7 eV allows for inelastic scattering of the electron pair. This opens up a decoherence channel and the correlation hole vanishes. Varying the primary energy is therefore a tool for tuning on or off decoherence effects.