1. Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, South Korea
2. Department of Physics and Astronomy, Seoul National University, Seoul 08826, South Korea
3. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
4. Department of Physics, Sogang University, Seoul 04107, South Korea
5. Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 37673, South Korea