1. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, P. R. China
2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China
3. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
4. Spallation Neutron Source Science Center, Dongguan 523803, P. R. China
5. Songshan Lake Materials Laboratory, Dongguan 523808, P. R. China
6. Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China