1. Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ 08544, USA.
2. Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
3. Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany.
4. Department of Physics and Astronomy, University of British Columbia (UBC), Vancouver, British Columbia V6T 1Z1, Canada.
5. Condensed Matter Physics and Materials Science, Brookhaven National Laboratory (BNL), Upton, NY 11973 USA.
6. Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA.
7. Central Research Institute of Electric Power Industry, Komae, 201-8511 Tokyo, Japan.