1. Institute for Advanced
Materials, Hubei Normal University, Huangshi 435002, P. R. China
2. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. China
3. Nanoscale Physics Research Laboratory,
School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom
4. College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, P. R. China
5. Hubei Collaborative Innovation Center for Rare Metal
Chemistry, Hubei Normal University, Huangshi 435002, P. R. China