1. Department of Physics, University of Science and Technology of China, Hefei 230026, China
2. Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
3. Key Laboratory of Strongly-Coupled Quantum Matter Physics, School of Physical Sciences, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China