1. DLR—Institute of Networked Energy Systems, Carl-von-Ossietsky Straße 15, 26129 Oldenburg, Germany
2. Institute of Physics, Chemnitz University of Technology, 09107 Chemnitz, Germany
3. Department of Physics and Earth Sciences, Jacobs University, Campus Ring 1, 28759 Bremen, Germany
4. Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang 790-784, South Korea