1. Biophysical Engineering Group, Max Planck Institute for Medical Research, Jahnstraße 29, D-69120 Heidelberg, Germany
2. Department of Physics and Astronomy, Heidelberg University, D-69120 Heidelberg, Germany
3. Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Jahnstraße 29, D-69120 Heidelberg, Germany
4. 2nd Physics Institute, University of Stuttgart, Im Pfaffenwaldring 57, D-70569 Stuttgart, Germany
5. Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany