1. Department of Physics, University of California–Davis, Davis, CA 95616, USA
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
3. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA
4. Department of Chemistry, University of Hawaii, Honolulu, Hawaii 96822, USA
5. Department of Materials Physics, Osaka University, Toyonaka, Osaka 560, Japan
6. Department of Physics, University of California–Berkeley, Berkeley, CA 94720, USA
7. Institut für Theoretische Physik, Universität Kiel, D-24118 Kiel, Germany