Dresden 2006 – wissenschaftliches Programm

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O: Oberflächenphysik

O 50: Time-resolved spectroscopy II

O 50.7: Vortrag

Freitag, 31. März 2006, 12:45–13:00, WIL C207

Mapping the electron correlation at surfaces by two-electron photoemission — •Frank O. Schumann, Carsten Winkler, Gwilherm Kerherve, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle

Established theoretical concepts show that the Coulomb and exchange interaction result in a tendency of two electrons to avoid each other leading to an exchange-correlation (xc) hole. We will report on double photoemission (DPE) experiments using a novel time-of-flight set-up consisting of a small central collector surrounded by a resistive anode. The first allows detection only within a narrow solid angle therefore fixing the momentum. The resistive anode covers a solid angle of ∼1 sr, the determination of the impact position results in momentum resolution. As pulsed light source we used synchrotron radiation and studied a NaCl(100) surface upon excitation with 34 eV photons. The very existence of coincidences is already a manifestation of the correlation. The onset of pair emission occurs, when energy conservation allows the ejection of two electrons from the highest occupied level. We have made two key observations. If E₁ and E₂ are fixed such that pair emission from the top of the valence band is possible, a zone of reduced intensity with a diameter of ∼1.1 Å⁻¹ is visible. Recent calculations on DPE from a Cu(100) surface display exactly such a feature due to the xc-hole. Hence we proof experimentally the very existence of the xc-hole in double photoemission.The zone of reduced intensity disappears, whenever emission below the top of the valence band becomes possible indicating the sensitivity of the xc-hole to inelastic scattering.