1. Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
2. Department of Materials Science and Engineering, University of California-Irvine, Irvine, California 92697, United States
3. Irvine Materials Research Institute, University of California-Irvine, Irvine, California 92697, United States
4. Department of Physics and Astronomy, University of California-Irvine, Irvine, California 92697, United States