1. Chair for Photonics and Optoelectronics, Department of Physics and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Amalienstrasse 54, 80799 Munich, Germany
2. Nanosystems Initiative Munich (NIM), Schellingstrasse 4, 80799 Munich, Germany
3. Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
4. Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (E), 81377 Munich, Germany
5. Lehrstuhl für Funktionelle Materialien, Physik Department, Technische Universität München, James-Franck-Strasse 1, 85748 Garching, Germany