1. Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 106, India.
2. Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
3. Research and Development Group, Hitachi Ltd., 1-280 Higashi-koigakubo, Kokubunji-shi, Tokyo 185-8601, Japan.
4. Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.