2School of Physics, Peking University, Chengfu Road 209, Haidian, Beijing 100871, China
3UCL Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
4Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing 100871, China
5Frontiers Science Center for Nano-Optoelectronics, Peking University, Beijing 100871, China
