1. Department of Applied Physics, Xi'an University of Technology 1 , Xi'an 710048, China
2. School of Electronic Science and Engineering, University of Electronic Science and Technology of China 2 , Chengdu, Sichuan 610054, China
3. School of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong 3 , Wollongong, NSW 2522, Australia