1. School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China
2. Key Laboratory of Special Function Materials and Structure Design, Ministry of Education, Lanzhou University, Lanzhou 730000, China
3. School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
4. School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China