1. Institute of Quantum Materials and Technologies, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
2. Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt, Germany
3. Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
4. Institute of Physical and Theoretical Chemistry, Julius Maximilian University Würzburg, Würzburg 97074, Germany
5. Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
6. Institute of Physical Chemistry, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany
7. Faculty of Physics, University of Sofia, 1164 Sofia, Bulgaria