1. Institute of Electrical and Microengineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015Lausanne, Switzerland
2. Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015Lausanne, Switzerland
3. Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015Lausanne, Switzerland
4. Chalmers University of Technology, Department of Physics, 412 96Gothenburg, Sweden
5. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
6. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
7. Philipps-Universität Marburg, Department of Physics, Renthof 7, D-35032Marburg, Germany