1. Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
2. IZM, Martin-Luther-Universität Halle-Wittenberg, Halle 06120, Germany
3. Institute für Physik, Martin-Luther-Universität Halle-Wittenberg, Halle 01620, Germany
4. Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1173, USA
5. Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511, USA