1. School of Electrical Engineering, The Key Lab of Magnetic Suspension Technique and Maglev Train of Railways, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
2. Key Laboratory of Advanced Technology of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
3. Ministry of Education of China, and Superconductivity and New Energy R&D Center, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
4. School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
5. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30318, USA
6. School of Physics and Energy, Fujian Normal University, Fuzhou, Fujian 351007, China