1. Shenzhen
Key Laboratory of Laser Engineering, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, P. R. China
2. Solid State Physics and Magnetism Section, KU Leuven, Celestijnenlaan 200 D, BE-3001 Leuven, Belgium
3. CMT & EMAT, Department of Physics, University of Antwerp, Groenenborgerlaan 171, BE-2020 Antwerp, Belgium
4. State Key Laboratory of Silicon Materials, Department
of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China