1. National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering; College of Engineering and Applied Science & Collaborative Innovation Center of Advanced Microstructures; Nanjing University; Nanjing 210093 China
2. Condensed Matter Science and Technology Institute; Harbin Institute of Technology; Harbin 150001 China
3. School of Materials Science and Engineering; Nanjing University of Science and Technology; Nanjing 210094 China