1. Department of physics, Veer Narmad South Gujarat University, Surat 395007, India
2. Condensed Matter Theory group, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, Uppsala 751-20, Sweden
3. Advanced Materials Lab, Department of Applied Physics, S.V. National Institute of Technology, Surat 395007, India
4. Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden