1. Department of Physics, National University of Defense Technology, Changsha, Hunan 410073, People’s Republic of China
2. Earth and Planets Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015, USA
3. Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721, USA
4. Quantum Theory Project, Department of Physics and Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA