1. Department of Physics, New York University, New York , New York 10012, USA
2. Departments of Physics and Mechanical Engineering and the Courant Institute of Mathematical Sciences, New York University, New York , New York 10012, USA
3. Department of Physics, Department of Geology, Institute for Research in Electronics and Applied Physics, and Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA