[1] Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA
[2] Natl High Magnet Field Lab, Tallahassee, FL 32310 USA
[3] Purdue Univ, Dept Phys & Astron, W Lafayette, IN 47907 USA
[4] Purdue Univ, Birck Nanotechnol Ctr, W Lafayette, IN 47907 USA
[5] Purdue Univ, Sch Mat Engn, W Lafayette, IN 47907 USA
[6] Purdue Univ, Sch Elect & Comp Engn, W Lafayette, IN 47907 USA
[7] Princeton Univ, Dept Elect Engn, Princeton, NJ 08544 USA