1. National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
2. School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China.
3. Department of Mechanical Engineering, University of Hong Kong, Pokfulam Road, Hong Kong.
4. American Physical Society, 100 Motor Pkwy, Hauppauge, NY 11788, USA.