1. Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan
2. Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
3. Department of Physics, School of Basic and Applied Sciences, Central University of Tamil Nadu, Thiruvarur 610005, Tamil Nadu, India
4. Department of Physics (MMV), Banaras Hindu University, Varanasi 221005, Uttar Pradesh, India
5. Department of Physics, National Taiwan University, Taipei 10617, Taiwan
6. Physics Division, National Center for Theoretical Sciences, Hsinchu 30013, Taiwan
7. Taiwan Semiconductor Research Institute, Hsinchu
Science Park, Hsinchu 300, Taiwan