1. Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20740, United States
2. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, United States
3. Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland 20740, United States
4. Department of Physics, University of Maryland, College Park, Maryland 20742, United States
5. U.S. Naval Research Laboratory, Washington, D.C. 20375, United States