1. Department of Physics, South China University of Technology, Guangzhou 510640, People’s Republic of China
2. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
3. National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China