1. Department of Physics, Center for Optoelectronics Engineering Research, Yunnan University, Kunming 650091, People’s Republic of China
2. Department of Materials Science and Engineering, University of Toronto, Toronto M5S 3E4, Canada
3. State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Frontiers Science Center for Nano-optoelectronics & Collaborative Innovation Center of Quantum Matter, Peking University, 100871 Beijing, People’s Republic of China