1. School of Physics and Electronics, Hunan Key Laboratory of Nanophotonics and Devices, Central South University, 932 South Lushan Road, Changsha 410083, Hunan, China
2. Powder Metallurgy Research Institute and State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, P. R. China
3. Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon 999077, Hong Kong, P. R. China
4. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China
5. Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310027, China