Xuetao Zhua,1, Yanwei Caoa,1, Jiandi Zhangb, E. W. Plummerb,2, and Jiandong Guoa,2
a Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
b Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70808
1 X.Z. and Y.C. contributed equally to this work.
2 To whom correspondence may be addressed.