1. Center
for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut 06520, United States
2. Department
of Applied Physics, Yale University, New Haven, Connecticut 06520, United States
3. Advanced
Materials Laboratory, Fudan University, Shanghai 200433, People’s Republic of China
4. Department
of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, United States
5. Department
of Physics, Yale University, New Haven, Connecticut 06520, United States