1. Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block − JD, Sector-III, Salt Lake, Kolkata 700 106, India
2. Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom
3. Institute of Engineering and Management, Sector-V, Salt Lake, Kolkata 700 091, India
4. London Centre for Nanotechnology, Imperial College London, London SW7 2AZ, United Kingdom