1. State Key Laboratory of Physical Chemistry of Solid Surfaces College of Chemistry and Chemical Engineering School of Electronic Science and Engineering Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM) Xiamen University Xiamen 361005 P. R. China
2. State Key Laboratory of Infrared Physics Shanghai Institute of Technical Physics Chinese Academy of Sciences Shanghai 200083 P. R. China
3. School of Physical Science and Technology ShanghaiTech University Shanghai 201210 P. R. China
4. The Laboratory of Soft Matter Physics Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 P. R. China
5. Center for the Physics of Low‐Dimensional Materials School of Physics and Electronics Henan University Kaifeng 475004 P. R. China
6. Department of Chemistry University of California Santa Barbara CA 93106 USA