1. School of Physics and Electronics, and Hunan Key Laboratory of Two-Dimensional Materials, Hunan University, Changsha 410082, P. R. China
2. Tianjin Key Laboratory of Functional Crystal Materials, Institute of Functional Crystal, School of Materials Science and Engineering, Tianjin University of Technology, Tianjin 300384, P. R. China
3. Key Laboratory for Special Functional Materials, Collaborative Innovation Center of Nano Functional Materials and Applications, Henan University, Kaifeng 475004, P. R. China