1. School of Physics, Peking University, Beijing 100871, P. R. China
2. Department of Chemistry, Fudan University, Shanghai 200438, P. R. China
3. Collaborative Innovation Center of Quantum Matter, Beijing 100871, P. R. China
4. Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing 100871, P. R. China
5. Frontiers Science Center for Nano-Optoelectronics, Peking University, Beijing 100871, P. R. China