1. Beijing
National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2. School
of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
3. Department
of Physics and the Quantum Theory Project, University of Florida, Gainesville, Florida 32611, United States
4. School
of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China