1. School of Optical and Electronic Information, and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei, China.
2. School of Aerospace Engineering, Beijing Institute of Technology, Beijing, China.
3. School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, China.
4. Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA.
5. Institute of Physics, Chinese Academy of Sciences, Beijing, China.
6. Hubei Key Laboratory of Ferro- & Piezoelectric Materials and Devices, Faculty of Physics and Electronic Science, Hubei University, Wuhan, Hubei, China.