Department of Applied Physics Nanjing University of Science and Technology Nanjing 210094 China;
Department of Applied Physics Nanjing University of Science and Technology Nanjing 210094 China;
Department of Applied Physics Nanjing University of Science and Technology Nanjing 210094 China;
Department of Physics State University of New York Buffalo 14260-1500 USA;
Department of Applied Physics Nanjing University of Science and Technology Nanjing 210094 China;