1. Peter Grünberg Research Centre, Nanjing University of Posts and Telecommunications, Nanjing 210003, China
2. GaN Optoelectronic Integration International Cooperation Joint Laboratory of Jiangsu Province, Nanjing 210003, China
3. Key Laboratory of Materials Physics, Institute of Solid State Physics, CAS, Hefei 230031, China
4. University of Science and Technology of China, Hefei 230031, China
5. High Magnetic Field Laboratory, CAS, Hefei 230031, China