1. Department of Physics, University of Arizona, Tucson, AZ 85721, USA.
2. Department of Material Science and Engineering, The Ohio State University, Columbus, OH 43210, USA.
3. Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany.
4. Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH 43210, USA.
5. Department of Physics, The Ohio State University, Columbus, OH 43210, USA.