1. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA 02139 USA
2. Center for Nanoscale Systems Harvard University Cambridge MA 02138 USA
3. Department of Physics University of California San Diego La Jolla CA 92093 USA
4. Carl Zeiss Microscopy LLC Peabody MA 01960 USA
5. Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore
6. Department of Physics Massachusetts Institute of Technology Cambridge MA 02139 USA
7. Department of Electrical Engineering The Pennsylvania State University University Park PA 16802 USA
8. National Institute for Materials Science Namiki 1‐1 Tsukuba Ibaraki 305‐0044 Japan
9. Department of Physics Columbia University New York NY 10027 USA