1. Center for Spintronics, Korea Institute of Science and Technology, Seoul 02792, South Korea
2. Department of Nanomaterials Science and Engineering, Korea University of Science and Technology, Daejeon 34113, South Korea
3. Department of Materials Science and Engineering, Yonsei University, Seoul 03722, South Korea
4. Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang University of Science and Technology, Pohang 37673, South Korea
5. KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, South Korea