1. Theoretical Sciences Unit; Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR); Jakkur P.O.; Bangalore 560 064 India
2. Department of Physics; Pondicherry University; Kalapet; Puducherry 605014 India
3. Chemistry and Physics of Materials Unit; Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR); Jakkur P.O.; Bangalore 560 064 India
4. International Centre for Materials Science and Sheik Saqr Laboratory; Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR); Jakkur P.O.; Bangalore 560 064 India