1. Fachbereich Physik, Philipps Universität Marburg, 35037 Marburg, Germany
2. CIC biomaGUNE, 20009 San Sebastian, Spain
3. Institute of Applied Physics and Institute of Toxicology and Genetics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
4. Instituto de Nanociencia de Aragon, University of Zaragoza, 50018 Zaragoza, Spain
5. Instituto de Ciencia de Materiales de Aragon, CSIC/University of Zaragoza, 50018 Zaragoza, Spain
6. Department of Physics, University of Illinois at Urbana—Champaign, Urbana, Illinois 61801, United States