Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 55: Time-resolved spectroscopies II

O 55.1: Vortrag

Donnerstag, 26. März 2009, 15:00–15:15, SCH A315

Quantum-beat spectroscopy of image-potential resonances — •Manuel Marks, Christian Schwalb, Kai Schubert, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität Marburg, D-35032 Marburg

Previous 2PPE studies of image-potential states on metal surfaces have largely concentrated on states that are located in a gap of the projected bulk band. In these cases, the states decay by inelastic electron-hole-pair excitation. In many situations of more practical interest, however, the resonant charge transfer at metal interfaces is more important. In this contribution we report the first results of a systematic 2PPE investigation of the image-potential states of Ag(111) where the states (n≥ 2) are degenerate with the upper sp-band of the metal. Although one might expect a rapid delocalization of electrons excited to these image-potential resonances, a whole series could be observed by coherent excitation of resonances up to quantum number n=7, just like in the well-studied case of the gap states of Cu(100). The binding energies E_n deduced from quantum-beat spectroscopy fit well to a Rydberg series with a quantum defect a=0.062. The inelastic lifetimes of the resonances show good agreement with the n³-scaling law. Surprisingly, the absolute values of the experimental lifetimes are longer than expected theoretically. A major difference between the Cu(100) image-potential states and the Ag(111) image-potential resonances is a considerably shorter dephasing time of the latter.