1. Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706, United States
2. State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
3. Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
4. RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan