1. Department of Physics
and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, United States
2. Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
3. Department
of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
4. Department of Materials Science and Engineering,
Department of Physics and Astronomy, and Department of Mechanical
Engineering, Johns Hopkins University, Baltimore, Maryland 21218, United States