[1] Nanjing Univ, Natl Lab Solid State Microstruct, Nanjing 210093, Jiangsu, Peoples R China
[2] Nanjing Univ, Dept Mat Sci & Engn, Nanjing 210093, Jiangsu, Peoples R China
[3] Nanjing Univ, Dept Phys, Nanjing 210093, Jiangsu, Peoples R China
[4] Nanjing Univ, Collaborat Innovat Ctr Adv Microstruct, Nanjing 210093, Jiangsu, Peoples R China