1. High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA
2. Center for Integrated Nanotechnologies and Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
3. Materials Research Program and The Texas Materials Institute, University of Texas at Austin, Texas 78712, USA
4. Department of Physics, South University of Science and Technology of China, Guangdong 518055, China