1. College
of Physics Science, Key Laboratory of Photonics Materials and Technology
in Universities of Shandong, Qingdao University, Ningxia Road, Qingdao Shinan District
No. 22, Qingdao 266071, China
2. National
Laboratory of Solid State Microstructures, Physics School, Nanjing University, Nanjing 210093, China
3. Beijing
National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China