1. Department of Materials Science and Engineering & Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Unit 3136, Storrs, Connecticut 06269-3136, United States
2. Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
3. Ames Laboratory & Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States
4. Institute of Theoretical Physics, Goethe University, D-60438 Frankfurt am Main, Germany