1. School of Physics and Technology, Wuhan University, Wuhan 430072, China
2. Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
3. Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, United States
4. Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States