1. National Laboratory of Solid State Microstructures Jiangsu Key Laboratory of Artificial Functional Materials College of Engineering and Applied Sciences Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 P. R. China
2. Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials School of Electronic Science and Engineering Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 P. R. China
3. Department of Physics Southeast University Nanjing 211189 P. R. China
4. School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 P. R. China
5. Wuhan National High Magnetic Field Center and School of Physics Huazhong University of Science and Technology Wuhan 430074 P. R. China