1. High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, Anhui, People's Republic of China
2. Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, People's Republic of China
3. National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China