1. Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanotechnology, CAS Center for Excellence in Nanoscience, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, P. R. China
2. University of Science and Technology of China, Hefei 230026, P. R. China
3. Institute of Physical Science and Information Technology, Anhui University, Hefei 230601, P. R. China
4. Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong 999077, P. R. China
5. Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, P. R. China
6. MOE Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University, Beijing 100084, P. R. China