**Acknowledgements**

The authors are thankful to the Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India, for granting permission to publish this work. Kaweri Gambhir acknowledges financial support from Dr. D. S. Kothari Postdoctoral Research Fellowship, University Grant Commission, India, through Grant No. No. F.4-2/2006 (BSR)/PH/19-20/0097.
