1. Department of Physics, University of Florida, Gainesville, Florida 32611, United States
2. Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14850, United States
3. Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14850, United States
4. School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, 200240, China
5. Mechanical Engineering, Sungkyunkwan University, 2066 Seoburo Jangan-gu, Suwon, Gyeonggi-do 16419, Korea
6. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14850, United States