[1] Univ Sci & Technol China, Struct Res Lab, Hefei 230026, Peoples R China
[2] Chinese Acad Sci, Hefei 230026, Peoples R China
[3] Univ Sci & Technol China, Dept Phys, Hefei 230026, Peoples R China
[4] Univ Sci & Technol China, Ctr Fundamental Phys, Hefei 230026, Peoples R China