1. School of Materials State Key Laboratory of Optoelectronic Materials and Technologies Sun Yat‐sen University Guangzhou 510275 P. R. China
2. State Key Laboratory of Infrared Physics Shanghai Institute of Technical Physics Chinese Academy of Sciences 500 Yutian Road Shanghai 200083 P. R. China
3. Hangzhou Institute for Advanced Study University of Chinese Academy of Sciences Hangzhou 310024 P. R. China