1. Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
2. Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, Bern 3012, Switzerland
3. Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, Karlsruhe 76131, Germany