[1] MIT, Dept Elect Engn & Comp Sci, Cambridge, MA 02139 USA
[2] Univ Fed Ceara, Dept Fis, BR-60455760 Fortaleza, Ceara, Brazil
[3] Tohoku Univ, Dept Phys, Sendai, Miyagi 9808578, Japan
[4] JST, CREST, Aoba Ku, Sendai, Miyagi 9808578, Japan
[5] MIT, Francis Bitter Natl Magnet Lab, Cambridge, MA 02139 USA
[6] MIT, Dept Phys, Cambridge, MA 02139 USA