1. Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588, USA
2. Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
3. Department of Physics, South Dakota State University, Brookings, South Dakota 57007, USA
4. Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
5. School of Basic Sciences, Indian Institute of Technology, Mandi, Himachal Pradesh 175001, India