1. High
Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 Anhui, People’s Republic of China
2. University of Science and Technology of China, Hefei 230026, Anhui, People’s Republic of China
3. Institute
of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, People’s Republic of China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People’s Republic of China
5. Department
of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118, United States
6. Department
of Physics and Material Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, United States