Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 50: Poster: Nanostructures on Surfaces II

O 50.7: Poster

Dienstag, 13. März 2018, 18:15–20:30, Poster B

Coupling of structural and electronic properties in 4/3-ML Pb/Si(111) investigated by femtosecond time- and angle-resolved 2PPE — •Abdul Samad Syed, Manuel Ligges, Vesna Mikšić Trontl, Peter Kratzer, and Uwe Bovensiepen — Fakultät für Physik, Universität Duisburg-Essen, Germany

Electronic properties and atomic structure of low dimensional systems determine each other. Scattering at steps was found, e.g., for Pb/Si(557) to lead to different electron relaxation for step down and step up directions [1]. A related, problem appears for threefold symmetry of Pb/Si(111)-(√3×√3) and we report here on the unoccupied electronic structure along [1 1 2] and [11 2] investigated by femtosecond time- and angle-resolved two photon photoemission (2PPE). Three electronic features dispersing along k_x ∥ [1 1 2] were identified with binding energies 3.65, 3.5, and 3.3 eV above the Fermi level. In angle-resolved measurements the observed electronic states show for opposite momenta k_x>0 and k_x<0, an asymmetric intensity I(k_x) and the electronic structure that appears to be different. In time-resolved experiment we find a momentum dependent change in the electron relaxation time τ(k_x). Polarization dependent studies reveal a different orbital character for the different states and for opposite k_x. We conclude to have identified the unidirectional anisotropy in the real and imaginary part of the electron self energy originating from the threefold surface symmetry of Pb/Si(111)-(√3×√3).

This work is funded by the DFG through research unit FOR 1700.

[1] A. Samad Syed et al., Phys. Rev. B 92, 134301 (2015).