1. Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
2. Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
3. Fakultät für Physik, Universität Bielefeld, 33615 Bielefeld, Germany
4. Department of Chemistry, Missouri University of Science & Technology, Rolla, Missouri 65409, United States
5. Department of Materials Science & Engineering, Missouri University of Science & Technology, Rolla, Missouri 65409, United States