1. a State Key Laboratory of Electronic Thin Films and Integrated Devices , University of Electronic Science & Technology of China , Chengdu, Sichuan, 610054, P. R. China
2. b Department of Physics and Astronomy , University of Texas at San Antonio , San Antonio, Texas, 78249, USA
3. c Department of Physics and The Texas Center for Superconductivity , University of Houston , Houston, Texas, 77204, USA