1. TUM School of Natural Sciences, Department of Physics, Chair for Functional Materials, Technical University of Munich, James-Franck-Str. 1, 85748 Garching, Germany
2. Walter Schottky Institute, Technische Universität München, 85748 Garching, Germany
3. Physics Department, TUM School of Natural Sciences, Technische Universität München, 85748 Garching, Germany
4. Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg (HI ERN), Immerwahrstraße 2, 91058 Erlangen, Germany
5. School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
6. Technical University of Munich, Heinz Maier-Leibnitz-Zentrum (MLZ), Lichtenbergstr. 1, 85748 Garching, Germany