1. State Key Laboratory of Superhard Materials, College of Physics, Jilin University 1 , Changchun, Jilin 130012, China
2. Center for High Pressure Science and Technology Advanced Research (HPSTAR) 2 , Changchun 130012, China
3. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences 3 , Beijing 100190, China
4. Department of Physics and Engineering Physics, Morgan State University 4 , Baltimore, Massachusetts 21251, USA