1. Department of Physics, University of Texas at Austin, Austin, TX 78712, USA.
2. Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10617, Taiwan.
3. State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, People’s Republic of China.
4. Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
5. Research Center for Applied Sciences, Academia Sinica, Taipei 10617, Taiwan.
6. School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
7. Department of Physics, National Taiwan University, Taipei 10617, Taiwan.