1 College of Engineering and Applied Sciences, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210023, China
2 School of Physics, Nanjing University, Nanjing 210023, China
3 Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
4 Hefei National Laboratory, Hefei 230088, China
5 Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing University, Nanjing 210023, China