1. Beijing National Laboratory
for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
2. College of Material, Chemistry
and Chemical Engineering, Hangzhou Normal University, Hangzhou, Zhejiang 310036, China
3. Department of Physics, Jiangxi Normal University, Nanchang 330022, China
4. Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States
5. School of Materials Science
and Engineering, Chonnam National University, Gwangju, 500-757, Republic of Korea