1. School of Microelectronics, University of Science and Technology of China, Hefei 230026, China
2. School of Integrated Circuits, Huazhong University of Science and Technology, Wuhan 430074, China
3. Faculty of Physics and Electronic Engineering, Jiangsu University, Zhenjiang 212013, China
4. Department of Electrical and Computer Engineering, Auburn University, Auburn, Alabama 36849, United States
5. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
6. Department of Applied Physics, Stanford University, Stanford, California 94305, United States
7. Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
8. Institute of Physics, Johannes Gutenberg University Mainz, D-55099 Mainz, Germany