1. Department of Physics, Carnegie Mellon University, Pittsburgh 15213, Pennsylvania, United States
2. Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy 12180, New York, United States
3. Department of Physics, School of Physical Science and Technology, Xiamen University, Xiamen 361005, China
4. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
5. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
6. Department of Physics, University of Texas at Dallas, Richardson 75080, Texas, United States
7. Department of Physics, Washington University in St Louis, St. Louis 63105, Missouri, United States