1. Key Laboratory of Materials PhysicsAnhui Key Laboratory of Nanomaterials and NanostructuresCAS Center for Excellence in NanoscienceInstitute of Solid State PhysicsChinese Academy of Sciences Hefei Anhui 230031 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 230026 China