1. School of Physics and Electronic Information Engineering, Engineering Research Center of Nanostructure and Functional Materials, Ningxia Normal University, Guyuan, Ningxia 756000, P. R. China
2. State Key Laboratory of Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
3. College of Mechanical and Material Engineering, North China University of Technology, Beijing 100144, P. R. China
4. Collaborative Innovation Center of Quantum Matter, Beijing 100871, P. R. China