1. Department
of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
2. Department
of Physics, Tohoku University, Sendai 980-8578, Japan
3. College
of Sciences, Liaoning Shihua University, Fushun 113001, China
4. Department
of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
5. Department
of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
6. Center
for
Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
7. Shenyang
National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China