1. Department of Physics, Renmin University of China, Beijing 100872, China
2. Songshan Lake Materials Laboratory, Dongguan 523808, Guangdong, China
3. Dongguan Academy of Advanced Ceramics and Composite Materials, Dongguan 523722, China
4. Fujian Key Laboratory of Nanomaterials Fujian Institute of Research on the Structure of Matter Chinese Academy of Sciences, Fuzhou 350002, China
5. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China