1. Center for Nanophysics
and Advanced Materials, University of Maryland, College Park, Maryland 20742-4111, United States
2. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, United States
3. Texas A&M University, Galveston, Texas 77553, United States
4. U.S. Naval Research Laboratory, Washington, D.C. 20375, United States
5. School of
Physics, Monash University, Victoria 3800, Australia