1. Department of Electrical Engineering, University of California, Los
Angeles, California 90095, United States
2. Beijing National Laboratory for Condensed
Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
3. State Key
Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
4. Collaborative Innovation Center of Quantum Matter, Beijing 100084, China