1. Shenzhen Geim Graphene Center and Institute of Materials Research, Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, People’s Republic of China
2. State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China
3. School of Materials Science and Engineering, Beihang University, Beijing 100191, People’s Republic of China
4. Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, Hamburg 22761, Germany
5. Institute for Advanced Study, Tsinghua University, Beijing 100084, People’s Republic of China
6. Frontier Science Center for Quantum Information, Beijing 100084, People’s Republic of China