1. Department of Macromolecular Structures, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, 28049 Cantoblanco, Madrid, Spain
2. Department of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
3. Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
4. Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
5. IFIMAC - Condensed Matter Physics Center, Universidad Autónoma de Madrid, E-28049 Madrid, Spain