1. Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
2. Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
3. Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China