Depantment of Physics;
Fujian Normal University Fuzhou 350007;
China;
National Laboratory of Solid State Microstructure;
Department of Physics;
Nanjing University;
Nanjing 210093;
China;
Center for Materials Analysis;
Nanjing University;
Nanjing 210093;
China;
Depantment of Physics;
Fujian Normal University;
Fuzhou 350007;
China;