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O: Oberflächenphysik

O 28: Postersitzung (Elektronische Struktur, Grenzfläche fest-flüssig, Halbleiteroberflächen und -grenzflächen, Magnetismus und Symposium SYXM, Methodisches, Nanostrukturen, Oberflächenreaktionen, Teilchen und Cluster, Zeitaufgelöste Spektroskopie)

O 28.72: Poster

Mittwoch, 10. März 2004, 16:00–19:00, Bereich C

Time development of electronic excitations of CO on MgO(001) — •N.-P. Wang¹, M. Rohlfing², P. Krüger¹, and J. Pollmann¹ — ¹Institut für Festkörpertheorie, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster — ²School of Engineering and Science, International University Bremen, P.O. Box 750761, 28725 Bremen

Femtosecond laser excitation is a very useful tool for acquiring important knowledge about the short-time dynamics of surface excitations. In this context the fundamental question arises how fast an initially localized excitation, which is not an eigenstate of the surface system but rather defines the ’initial value’ of the time-dependent Schrödinger equation, develops in space and time. Here the dependence of the time decay on the initial molecular excitation and the electronic spectrum of the substrate surface is of particular interest. We have studied therefore the dynamics of electronic excitations in a CO adlayer on MgO(001)-(1×1) from first principles. One-particle excitations of the ground state, described within DFT-LDA, are calculated employing the GW approximation. Two-particle excitations and their optical spectrum are obtained solving the Bethe-Salpeter equation including electron-hole interaction. The time evolution of the molecular excitation is then determined from the time-dependent Schrödinger equation. An initial CO exciton state is found to decay exponentially within two femto-seconds after coupling the adlayer to the substrate. This is due to a resonance with charge-transfer excitations between the substrate and the adlayer. Interestingly, the decay of the molecular exciton is an order of magnitude faster than the decay of single-particle states.