1. Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712, USA
2. Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
3. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, 48109, USA
4. Department of Physics, Arizona State University, Tempe, Arizona 85287-1504, USA