Ding, S.Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China Jia, B.Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China Li, F.Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China Zhu, Z.Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China