1. Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India
2. Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Center, Mumbai 400085, India
3. National Institute for Materials Science, Tsukuba, Ibaraki 305-0003
4. Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08855, U.S.A.