1. National Laboratory of Solid State Microstructures
2. School of Physics
3. Collaborative Innovation Center of Advanced Microstructures
4. Nanjing University
5. Nanjing 210093
6. Department of Materials Science and Engineering
7. Nanjing
8. Key Laboratory of Polar Materials and Devices
9. Ministry of Education
10. East China Normal University
11. Shanghai 200062
12. China