1. College of Physics, Chongqing University, Chongqing 401331, China.
2. Department of Mathematical Sciences, Tsinghua University, Beijing 100084, China.
3. Department of Physics, Key Laboratory of Micro- and Nano-Photonic Structures (MOE), and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China.
4. Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.