1. Department of Physics, Chemistry and Biology; Linköping University; Linköping S-581 83 Sweden
2. Graduate Program of Materials Science and Engineering; University of California; San Diego, La Jolla CA 92093 USA
3. Department of Physics; University of California; San Diego, La Jolla CA 92093 USA
4. Department of Electrical and Computer Engineering; University of California; San Diego, La Jolla CA 92093 USA