1. State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Material and Technology, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China.
2. Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
3. Institute of Physics, Chinese Academy of Science and Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.
4. School of Physical Sciences, University of Chinese Academy of Science, Beijing 100049, China.
5. Center for Nanoscale Systems, Harvard University, Cambridge, MA 02138, USA.