1. Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
2. Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
3. Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
4. Center for Theoretical and Computational Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
5. Center of Crystal Research, National Sun Yat-sen University, Kaohsiung 80424, Taiwan