1. Key
Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials
and Nanostructures, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China
2. Department
of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China
3. Hefei
National Laboratory for Physics Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China