1. State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics Tsinghua University Beijing 100084 China
2. Department of Materials Science and Engineering National Chiao Tung University Hsinchu 30010 Taiwan
3. Advanced Light Source Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
4. Department of Physics Durham University Durham DH13LE UK
5. Collaborative Innovation Center of Quantum Matter Beijing 100084 China
6. RIKEN Center for Emergent Matter Science (CEMS) Wako 351‐198 Japan