1. State Key Laboratory of Electronic Thin films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, People’s Republic of China
2. Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
3. Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249, USA and Department of Physics and the Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA