1. Key Lab of Artificial Micro‐ and Nano‐Structures of Ministry of Education of ChinaSchool of Physics and TechnologyWuhan University Wuhan Hubei 430072 P. R. China
2. Center for Nanoscale Characterization & Devices (CNCD)Wuhan National Laboratory for Optoelectronics (WNLO)School of PhysicsHuazhong University of Science and Technology (HUST) Wuhan Hubei 430074 P. R. China
3. School of ScienceEast China University of Science and Technology Shanghai 200237 P. R. China