1. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
2. Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
3. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
4. Department of Geological Sciences, Stanford University, Stanford, California 94305, United States