1. Department of Applied Physics, School of Physics and Electronics, Hunan University, Changsha 410082, China
2. School of Materials and Environmental Engineering, Changsha University, Changsha 410082, China
3. College of Materials Science and Engineering, Hunan University, Changsha 410082, China
4. Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109, United States