1. School of Physics and Astronomy; The University of Nottingham; Nottingham NG7 2RD UK
2. Institute of Microelectronics Technology and High Purity Materials; RAS; Chernogolovka 142432 Russia
3. Laboratoire National des Champs Magnétiques Intenses; CNRS-UGA-UPS-INSA-EMFL; 25 rue des Martyrs 38042 Grenoble France
4. Institute for Problems of Materials Science; The National Academy of Sciences of Ukraine; Chernivtsi Branch Chernivtsi 58001 Ukraine
5. School of Physics and Astronomy; University of Manchester; Oxford Road Manchester M13 9PL UK
6. National Graphene Institute; University of Manchester; Oxford Road Manchester M13 9PL UK
7. State Key Laboratory of Physical Chemistry of Solid Surface; College of Chemistry and Chemical Engineering; Collaborative Innovation Center of Chemistry for Energy Materials; Xiamen University; Xiamen 361005 China
8. Department of Physics; Tohoku University; Sendai 980-8578 Japan