1. Department of Chemical, Biological and Macromolecular Sciences; S. N. Bose National Centre for Basic Sciences; Block JD, Sector III, Salt Lake Kolkata 700 106 India
2. Dept. of Electrical Engineering; Indian Institute of Technology Bombay, Powai; Mumbai 400 076, Maharashtra India
3. Institute for Condensed Matter Physics; TU Braunschweig; Mendelssohnsstr 3 38106 Braunschweig Germany