Thomas Fauster, Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg
The screening of external charges by a two-dimensional electron gas is
studied by spectroscopy of loosely bound electrons on graphene grown
on various substrates. The charge transfer from the substrate to the
graphene layer (doping) is correlated with the work function and the
energy of the Dirac point in good agreement with theoretical
predictions [1]. The spectroscopy of the unoccupied states by
two-photon photoemission reveals that the long-range image potential
applies only for energies close to the vacuum level [2]. The lowest
state is found at 3.7 eV above the Dirac point independent of the
substrate. This indicates that for this state the screening is
dominated by the electronic structure of the graphene layer.
Two-photon photoemission from bismuth chalcogenides reveals
unoccupied topological surface states in addition to the well known
states near the Fermi level. The spin structure of these states is
studied by circular dichroism.
[1] P. A. Khomyakov et al., Phys. Rev. B 79, 195425 (2009).
[2] D. Niesner et al., Phys. Rev. B 85, 081402 (2012).