1. Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511, United States
2. Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, United States
3. Department of Physics, The University of Texas at Dallas, Richardson, Texas 7508, United States
4. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
5. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan