1. School of Physics, Shandong University, Jinan, 250100, China, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, China, Graduate School of the Chinese Academy of Sciences, Beijing 100080, China, Department of Physics, Zhejiang Normal University, 321004, Jinhua, China, and Theoretical Physics Center for Science Facilities (TPCSF), CAS, 19(B) Yuquan Road, Beijing 100049, China