1. State Key Laboratory of Crystal Materials and Institute of Crystal Materials Shandong University Jinan 250100 P. R. China
2. Jinan Institute of Quantum Technology Jinan 250101 P. R. China
3. School of Physics Shandong University Jinan 250100 P. R. China
4. Advanced Materials Institute Qilu University of Technology (Shandong Academy of Sciences) Jinan 250014 P. R. China