1. School of Physics and Materials Science, Guangzhou University, Guangzhou 510006, China
2. National Laboratory of Solid State Microstructures, College of Engineering and Applied Science & Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing University, Nanjing 210093, China
3. Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China
4. Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong, China