1. Key Laboratory of Materials PhysicsAnhui Key Laboratory of Nanomaterials and NanotechnologyCAS Center for Excellence in NanoscienceInstitute of Solid State PhysicsChinese Academy of Sciences Hefei 230031 P. R. China
2. Institute of Physical Science and Information TechnologyAnhui University Hefei 230601 China
3. Hefei National Laboratory for Physical Sciences at the MicroscaleUniversity of Science and Technology of China Hefei Anhui 230026 P. R. China
4. Tsinghua University-Peking University Joint Center for Life SciencesSchool of Life SciencesTsinghua University Beijing 100084 P. R. China
5. MOE Key Laboratory of BioinformaticsSchool of Life SciencesTsinghua University Beijing 100084 P. R. China