1. MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing100081, China
2. School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
3. Institute of Microstructure and Property of Advanced Materials, Beijing Key Lab of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing100124, China
4. College of Physics and Electrical Information Engineering, Daqing Normal University, Daqing163000, P. R. China