1. State Key Laboratory of Low-Dimensional Quantum Physics; Department of Physics and Tsinghua-Foxconn Nanotechnology Research Center; Tsinghua University; Beijing 100084 China
2. State Key Laboratory for Mesoscopic Physics; School of Physics; Peking University; Beijing 100871 China
3. National Laboratory for Infrared Physics; Shanghai Institute of Technical Physics; Chinese Academy of Sciences; 500 Yu Tian Road Shanghai 200083 China
4. Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education; Department of Chemistry; Tsinghua University; Beijing 100084 China
5. State Key Laboratory for Superlattice and Microstructures; Institute of Semiconductors; Chinese Academy of Sciences; Beijing 100083 China
6. State Key Laboratory of New Ceramics and Fine Processing; School of Materials Science and Engineering; Tsinghua University; Beijing 100084 China
7. Collaborative Innovation Center of Quantum Matter; Beijing 100084 China