1. Department of Physics, University of Washington, Seattle, WA 98195, USA.
2. Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
3. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
4. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
5. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
6. Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
7. Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
8. Department of Physics, University of Hong Kong, Hong Kong, China.