1. Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095, United States
2. Institute
of Physics, Academia Sinica, Taipei 115, Taiwan
3. Department of Physics and Center for Nanotechnology, Chung Yuan Christian University, Chungli 32023, Taiwan
4. Space and Naval Warfare (SPAWAR) Systems Center Pacific, San Diego, California 92152, United States
5. Physical
Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Kingdom of Saudi Arabia