1. Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, D-76131 Karlsruhe, Germany
2. Fraunhofer Institute for Applied Solid-State Physics (IAF), Tullastrasse 72, D-79108 Freiburg, Germany
3. University of Stuttgart (UST), Pfaffenwaldring 47, D-70569 Stuttgart, Germany