1. Department of Physics and Astrophysics, University of Delhi, New Delhi, India
2. Department of Physics, Miranda House, University of Delhi, New Delhi, India
3. Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Straße 11, 12489, Berlin, Germany
4. Department of Physics, Kirori Mal College, University of Delhi, New Delhi, India