[1] Beijing Univ Aeronaut & Astronaut, Dept Phys, Sch Sci, Beijing 100083, Peoples R China
[2] Nanjing Univ, Dept Phys, Natl Lab Solid State Microstruct, Ctr Adv Studies Sci & Technol Microstruct, Nanjing 210093, Peoples R China
[3] Nanjing Univ, Natl Lab Solid State Microstruct, Nanjing 210093, Peoples R China
[4] CCAST, World Lab, Beijing 100080, Peoples R China