作者机构:[1]Department of Physics, Ningbo University, Ningbo 315211, China
相关基金:Project supported by the National Natural Science Foundation of China (Grant Nos. 10675065, 90503006 and 10735030) and the K.C.Wong Magna Fund in Ningbo University.Acknowledgement The author would like to thank the helpful discussion of Prof. Sen-Yue Lou.