1. State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, P. R. China
2. Collaborative Innovation Center of Quantum Matter, Beijing 100871, P. R. China
3. Key Laboratory of Yunnan Higher Education Institutes for Optoelectric Information &Technology, Kunming 650500, P. R. China
4. State Key Laboratory of Mechanics and Control of Mechanical Structures and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, P. R. China