1. Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea
2. Department of Physics and Oxide Research Centre, Memory and Catalyst Research Center, Hankuk University of Foreign Studies, Yongin 17035, South Korea
3. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA
4. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA