[1] Indian Inst Technol, Dept Phys & Meteorol, Kharagpur 721302, W Bengal, India
[2] Hitachi Europe Ltd, Hitachi Cambridge Lab, Cambridge CB3 0HE, England
[3] Indian Inst Technol, Dept Elect Engn, Powai, India
[4] Leibniz Univ Hannover, Inst Elect Mat & Devices, D-30167 Hannover, Germany