1. Department of Physics, The Pennsylvania State University, University Park, Pennsylvania16802, United States
2. School of Physics, Zhejiang University, Hangzhou310058, People’s Republic of China
3. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
4. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
5. Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania16802, United States
6. Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania16802, United States