[1]Beijing National Laboratory for Condensed Matter Physics,Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China [2]Max-Planck-Institut ffir Festkorperforschung, Heisenbergstraβe 1, D-70569 Stuttgart, Germany
基金项目:
Project supported by the National Natural Science Foundation of China (Grant No. 10974242) and the National Basic Research Program of China (Grant No. 2011CBA00106).