1. 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
2. Institute of Experimental and Applied Physics, Kiel University, 24098 Kiel, Germany
3. Ruprecht Haensel Laboratory, Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
4. Max Planck Institute for Biophysical Chemistry (MPIBPC), Göttingen, Am Fassberg 11, 37077 Göttingen, Germany