[1] Nanjing Tech Univ, Coll Mat Sci & Engn, Nanjing 210009, Jiangsu, Peoples R China
[2] Xiangtan Univ, Dept Phys, Xiangtan 411105, Peoples R China
[3] Nanjing Univ, Dept Mat Sci & Engn, Nanjing 210093, Jiangsu, Peoples R China
[4] Nanjing Univ, Natl Lab Solid State Microstruct, Nanjing 210093, Jiangsu, Peoples R China