1. Department of Physics, Columbia University, New York, New York 10027, United States
2. Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
3. Condensed Matter Physics and Material Science Department, Brookhaven National Laboratory, Upton, New York 11973, United States
4. Research Center for Functional Materials, National Institute of Material Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
5. International Center for Materials Nanoarchitectonics, National Institute of Material Science, Namiki 1-1, Tsukaba, Ibaraki 305-0044, Japan
6. Department of Physics, University of California San Diego, La Jolla, California 92093, United States