1. Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
2. Physics and Chemistry of Nanostructures, Ghent University, 9000 Ghent, Belgium
3. Experimentelle Physik 2, Technische Universität Dortmund, 44227 Dortmund, Germany
4. High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The Netherlands
5. Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
6. Institut d’Électronique, de Microélectronique et de Nanotechnologie, UMR CNRS 8520, 59652 Villeneuve d’Ascq, France