1. School of Physics and Technology, Center for Ion Beam Application, Hubei Nuclear Solid Physics Key Laboratory, and MOE Key Laboratory of Artificial Micro- and Nano-Structures, Wuhan University, Wuhan 430072, P. R. China
2. Key Laboratory of Strongly-Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China