1Hubei Yangtze Memory Laboratories, Wuhan 430205, Hubei , China
2School of Physics and Technology, Wuhan University, Wuhan 430072, Hubei , China
3School of Microelectronics, Wuhan University, Wuhan 430072, Hubei , China
4Center for Nanoscience and Nanotechnology, and Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education, Wuhan University, Wuhan 430072, Hubei , China