[1] NYU, Dept Phys, New York, NY 10003 USA
[2] IBM TJ Watson Res Ctr, Yorktown Hts, NY 10598 USA
[3] Hitachi GST, San Jose Res Ctr, San Jose, CA 95135 USA
[4] Univ Calif San Diego, CMRR, La Jolla, CA 92093 USA
[5] Nancy Univ, IJL, CNRS, UMR 7198, F-54042 Nancy, France