1. Department
of Physics, University of Texas at Austin, Austin, Texas 78712, United States
2. Institute of Atomic and Molecular Sciences, Academia Sinica, No.
1, Roosevelt Road, Section 4, Taipei 10617, Taiwan
3. Physical
Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
4. Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States