1. Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
2. Department of Physics, The University of Hong Kong, Hong Kong, China
3. Materials Physics, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 16440 Kista, Sweden
4. Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden