1. School of Materials Engineering, Purdue University, West Lafayette, Indiana 47906, United States
2. School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47906, United States
3. Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47906, United States
4. Department of Physics and Astronomy, Aarhus University, Aarhus 8000, Denmark
5. National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan