1. College of Physics and Electronic Science, Hubei Normal University 1 , Huangshi 435002, China
2. School of Physics and Mechanical Electrical and Engineering, Hubei University of Education 2 , Wuhan 430205, China
3. Department of Physics, Zhejiang Sci-Tech University 3 , Hangzhou 310018, China
4. School of Physics, Huazhong University of Science and Technology 4 , Wuhan 430074, China
5. Laboratory of Solid State Microstructures, Nanjing University 5 , Nanjing 210093, China