1. Department of Physics National Cheng Kung University Tainan 70101 Taiwan
2. Department of Electrophysics National Chiao Tung University Hsinchu 30010 Taiwan
3. Key Laboratory of Polar Materials and Devices Ministry of Education Department of Electronics East China Normal University Shanghai 200241 China
4. National Synchrotron Radiation Research Center Hsinchu 30076 Taiwan
5. Max‐Planck Institute for Chemical Physics of Solids Dresden 01187 Germany
6. Center for Quantum Frontiers of Research & Technology (QFort) National Cheng Kung University Tainan 70101 Taiwan