1. HiPSEC & Physics Department, University of Nevada, Las Vegas, Nevada 89154, United States
2. Institute of Atomic & Molecular Physics, Sichuan University, Chengdu 610065, China
3. National
Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
4. Materials Science
and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
5. School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States