1. Department of Applied Physics, Chalmers University of Technology, 412 96 Göteborg, Sweden
2. School of Science and Technology, Örebro University, 701 82 Örebro, Sweden
3. Quantum Science Laboratory, School of Mathematics and Physics, The University of Queensland, St. Lucia, Brisbane, Queensland 4072, Australia
4. Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
5. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China