Hefei National Laboratory for Physical Sciences at Microscale;
Department of Modern Physics;
University of Science and Technology of China;
Hefei 230026 China;
Institute of Modern Physics;
Chinese Academy of Sciences;
Lanzhou 730070;
China;
Shanghai EBIT Laboratory;
Institute of Modern Physics;
Fudan University;
and the Key Laboratory of Applied Ion Beam Physics;
Chinese Ministry of Education;
Shanghai 200433;
China;