1. Department of Physics, Informatics and Mathematics, University of Modena and Reggio Emilia, 41125 Modena, Italy
2. Center S3, CNR Institute Nanoscience, Via Campi 213/A, 41125 Modena, Italy
3. FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
4. Department of Biomedical, Metabolic and Neural Sciences, and Centre for Neuroscience and Neurotechnology, University of Modena and Reggio Emilia, Via G. Campi 287, 41125 Modena, Italy
5. Department of Biochemistry, Science Institute, University of Iceland, Sturlugata 7, 102 Reykjavík, Iceland
6. Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, D-01307 Dresden, Germany
7. INFN Firenze, Via Sansone 1, 50019 Sesto Fiorentino, Italy