1. Department of Physics, Indian Institute of Technology (BHU), Varanasi 221005, India
2. Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
3. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
4. Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
5. Department of Physics, Banaras Hindu University, Varanasi 221005, India