1. Beijing National Laboratory for Condensed
Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, National Center for Nanoscience and
Technology (NCNST), Beijing 100083, China
3. Physics and
Electronic Technology, Hubei University, Wuhan, Hubei 430062, P. R. China
4. Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain
5. Institut Laue Langevin, BP 156X, Grenoble Cedex, France