[1] Guangdong Univ Technol, Dept Phys, Guangzhou 510006, Guangdong, Peoples R China
[2] Guangdong Univ Technol, Expt & Educ Ctr, Guangzhou 510006, Guangdong, Peoples R China
[3] S China Univ Technol, Dept Phys, Guangzhou 510640, Guangdong, Peoples R China