Pan Li,a Deng Pan,b Longkun Yang,a Hong Wei,c Shuli He,aHongxing Xubde and Zhipeng Li*a
a The Beijing Key Laboratory for Nano-Photonics and Nano-Structure (NPNS), Center for Condensed Matter Physics, Department of Physics, Capital Normal University, Beijing 100048, P.R. China
b School of Physics and Technology, Wuhan University, Wuhan 430072, P. R. China
c Beijing National Laboratory for Condensed Matter Physics, Institute of Physics Chinese Academy of Sciences, University of Physics Chinese Academy of Sciences, Collaborative Innovation Center of Quantum Matter, Beijing 100190, P. R. China
d The Institute for Advanced Studies, Wuhan University, Wuhan 430072, P. R. China
e Division of Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, Lund, Sweden