1. Department of Physics, Hebei Normal University, Shijiazhuang 050016, P. R. China
2. Hebei Advanced Thin Films Laboratory, Shijiazhuang 050016, P. R. China
3. Center for Nonlinear Studies and National Key Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100088, P. R. China
4. Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100088, P. R. China
5. Science and Technology Office of Hulunbeir College, Hailaer, Neimonggu 021008, P. R. China