1. Second Physics Institute, University of Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
2. Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
3. Fourth Physics Institute, University of Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
4. Wallace L. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, Georgia 30322 United States
5. Institute of Physics, University of Graz, and NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria