1. Center for Nanochemistry (CNC)Academy for Advanced Interdisciplinary StudiesDepartment of Materials Science and EngineeringCollege of EngineeringPeking University Beijing 100871 P. R. China
2. State Key Laboratory for Artificial Microstructure and Mesoscopic PhysicsPeking University Beijing 100871 P. R. China
3. Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of Sciences Beijing 100190 P. R. China
4. School of Physical SciencesUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
5. Collaborative Innovation Center of Quantum Matter Beijing 100190 P. R. China