1. Experimental Molecular Biophysics, Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany
2. Physikalisch-Technische Bundesanstalt, 38116 Braunschweig and 10587 Berlin, Germany
3. Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
4. SPINTEC, CEA, CNRS and Université Grenoble Alpes, 17 Rue des Martyrs, 38054 Grenoble, France
5. Institute of Physics ASCR, v.v.i., 162 53 Praha 6, Czech Republic
6. Hitachi Cambridge Laboratory, Cambridge CB3 0HE, United Kingdom