1. Department of Physics, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India
2. Department of Condensed Matter Physics and Material Science, S. N. Bose National Center for Basic Sciences, Block-JD, Salt Lake, Kolkata 700106, India
3. Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India
4. Chemistry & Bioinformatics Department, Terramera Inc., Vancouver, British Columbia V5Y 1K3, Canada