1. School of Physics, Nanjing University, Nanjing 210093, China
2. Solid State Microstructure National Key Lab and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
3. Department of Materials Science and Engineering, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China
4. National Center of Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA
6. Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China