1. Institute of Physics, Johannes Gutenberg University, Staudinger Weg 7, 55128 Mainz, Germany
2. CICECO – Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, 3810-093 Aveiro, Portugal
3. Graduate School of Excellence Materials Science in Mainz, Staudinger Weg 9, 55128 Mainz, Germany
4. Institute of Optics and Atomic Physics, Technical University of Berlin, Str. des 17 Juni 135, 10623 Berlin, Germany