1. National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
2. Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay,
Kowloon, Hong Kong, China
3. Department of Applied Physics, Research Institute for Smart Energy, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
4. Department of Materials Science and Engineering, Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697, United States