1. Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, People's Republic of China
2. Department of Basic Education, Qinghai University, Xining 810016, People's Republic of China
3. School of Mathematics and Physics, China University of Geosciences (Wuhan), Wuhan 430074, People's Republic of China
4. Department of Physics and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, USA