Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 67: Electronic structure of surfaces: Spectroscopy, surface states III

O 67.1: Hauptvortrag

Mittwoch, 14. März 2018, 15:00–15:30, MA 042

Ultrafast dynamics of two-dimensional electron systems probed by time- and angle-resolved two-photon photoemission — •Jens Güdde — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, 35032 Marburg

Two-dimensional (2D) electron systems have attracted interest for more than 40 years due to unique properties that have no counterpart in 3D. In this talk I will first report on a 2D electron gas with close to ideal properties for fundamental studies. Ultrathin He films on single-crystal metal surfaces allow for an isolation of the electron system from the bulk and at the same time achieve a relatively large binding energy due to a strong image-force interaction with the metal. Our results for a monolayer (ML) of He/Cu(111) let us extrapolate lifetimes of nanoseconds for only a few ML of He on substrates such as Cu(100) with binding energies that are still large enough to support electron densities up to the quantum regime without instabilities [1].

Topologically protected states at the surfaces of 3D topological insulators represent a model for relativistic 2D electron systems with a characteristic Dirac-like energy dispersion. Optical excitation with near-infrared light pulses offers the possibility to induce and control spin-polarized electrical surface currents without exciting the bulk electron system [2]. Our experiments reveal unusually long elastic decay times of these currents due to spin-momentum locking of the Dirac electrons.

[1] N. Armbrust et al. Phys. Rev. Lett. 116, 256801 (2016).
[2] K. Kuroda et al., Phys. Rev. Lett. 116, 076801 (2016).