1. Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
2. Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
3. Center for Theoretical and Computational Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
4. Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan