1. College of Materials & Environmental Engineering; Hangzhou Dianzi University; Hangzhou 310018 P. R. China
2. College of Physics and Energy; Fujian Normal University; Fuzhou 350117 P. R. China
3. Institute of High Energy Physics; Chinese Academy of Sciences; Beijing 100049 P. R. China
4. School of Materials Science and Engineering; Zhejiang University; Hangzhou 310027 P. R. China
5. College of Materials Science and Engineering; Kunming University of Science and Technology; Kunming 650093 P. R. China
6. Department of Materials Science and Engineering; University of North Texas; Denton TX 76207 United States
7. Department of Physics; University of Science and Technology of China; Hefei 230026 P. R. China