1. Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
2. Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, D-01187 Dresden, Germany
3. Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
4. Faculty for Physics and Astronomy (TP4), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
5. Department of Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland