1. Stanford Institute for Materials and Energy Sciences SLAC National Accelerator Laboratory Menlo Park CA 94025 USA
2. Department of Applied Physics Stanford University Stanford CA 94305 USA
3. Department of Physics Stanford University Stanford CA 94305 USA
4. School of Applied and Engineering Physics Cornell University Ithaca NY 14853 USA
5. Kavli Institute at Cornell for Nanoscale Science Cornell University Ithaca NY 14853 USA
6. Department of Physics City University of Hong Kong Kowloon Hong Kong