1. Center for Quantum Nanoscience, Institute for Basic Science (IBS), Seoul 03760, Korea
2. Ewha Womans University, Seoul 03760, Korea
3. International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People’s Republic of China
4. Department of Physics, Ewha Womans University, Seoul 03760, Korea
5. The Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan