1. Solid State Physics
Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
2. Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
3. Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
4. Advanced
Materials Laboratory, National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
5. National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom