1. Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
2. National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
3. Department of Photonics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
4. Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei 106, Taiwan