1. College of Mechanical and Material Engineering, North China University of Technology, Beijing 100144, P. R. China
2. State Key Laboratory of Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
3. Collaborative Innovation Center of Quantum Matter, Beijing 100871, P. R. China
4. Peking University Yangtze Delta Institute of Optoelectronics, Nantong 226000, P. R. China