1. Nano
Structural Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, Jiangsu, China
2. Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
3. IBM Research, Zurich, 8803 Rüschlikon, Switzerland
4. State
Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
5. Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
6. RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
7. Physics
and Materials Science Research Unit, University of Luxembourg, L-1511, Luxembourg