1. National Laboratory of Solid State Microstructures and Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
2. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
3. Department of Electronics and Physics, Nanjing-York Joint Center of Spintronics and Nano Engineering, University of York, York YO105DD, United Kingdom