1. Department of Physics, Philipps-Universität Marburg, Renthof 7, D-35032 Marburg, Germany
2. Department of Physics, University of Regensburg, Regensburg D-93053, Germany
3. Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany
4. Chalmers University of Technology, Department of Physics, 412 96 Gothenburg, Sweden
5. Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
6. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki 305-004, Japan
7. Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-004, Japan