1. Graduate
Institute of Photonics and Optoelectronics and Department of Electrical
Engineering, National Taiwan University, Taipei 10617, Taiwan
2. Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
3. Department
of Physics, King’s College London, Strand, London WC2R 2LS, U.K.
4. Material
and Chemical Research Laboratories, Industrial Technology Research Institute, Hsin-Chu 31040, Taiwan
5. Center
for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
6. Computer, Electrical and Mathematical Sciences and Engineering Division, King Abdullah University of Science & Technology, Thuwal 23955-6900, Saudi Arabia
7. Department
of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854, United States
8. Department
of Physics, National Taiwan University, Taipei 10617, Taiwan