1. National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
2. Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
3. Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
4. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States