1. Department of PhysicsSouthern University of Science and Technology Shenzhen 518055 P. R. China
2. Department of Materials Science and EngineeringSouthern University of Science and Technology Shenzhen 518055 P. R. China
3. Department of PhysicsThe University of Hong Kong Pokfulam 999077 Hong Kong
4. State Key Laboratory of Surface PhysicsKey Laboratory of Micro and Nano Photonic Structuresand Department of PhysicsFudan University Shanghai 200433 China
5. International Collaborative Laboratory of 2D Materials for Optoelectronics Science and TechnologyKey Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province and College of Optoelectronic EngineeringShenzhen University Shenzhen 518060 P. R. China
6. Shenzhen Institute for Quantum Science and EngineeringSouthern University of Science and Technology Shenzhen 518055 P. R. China
7. Shenzhen Key Laboratory of Quantum Science and Engineering Shenzhen 518055 P. R. China