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