1. Center for High Pressure Science and Technology Advanced Research; Shanghai 201203 China
2. Key Laboratory of High-Temperature and High-Pressure Study of the Earth's Interior; Institute of Geochemistry; Chinese Academy of Sciences; Guiyang Guizhou 550081 China
3. Department of Materials Science and Engineering; University of California; Berkeley CA 94720 USA
4. State Key Laboratory for Superhard Materials; Institute of Atomic and Molecular Physics; Jilin University; Changchun 130012 China
5. Department of Physics; and Collaborative Innovation Center of Advanced Microstructures; Nanjing University; Nanjing 210093 China
6. Geophysical Laboratory; Carnegie Institution of Washington; Wangshiton DC 20015 USA