1. Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
2. Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
3. Department of Physics and Astronomy, Howard University, Washington, DC 20059, United States
4. Department of Physics, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece