1. Experimental Physics II, Institute of Physics, University of Augsburg, 86159 Augsburg, Germany
2. School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
3. ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
4. Shanghai Key Laboratory of High-resolution Electron Microscopy and ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China