1. School of Physics and Electrical Information, Shangqiu Normal University, Henan 476000, P. R. China
2. Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092, P. R. China
3. School of Energy and Machinery Engineering, Jiangxi University of Science and Technology, Nanchang 330013, P. R. China