1. National Laboratory of Solid-State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
2. Department of Applied Physics, College of Science, Nanjing Forestry University, Nanjing 210037, China
3. School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
4. Institute for Advanced Materials, Hubei Normal University, Huangshi 435002, Hubei, China