[1] Princeton Univ, Dept Elect Engn, Princeton, NJ 08544 USA
[2] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[3] Harvard Univ, Dept Phys, Cambridge, MA 02138 USA
[4] CUNY Coll Staten Isl, Dept Engn Sci & Phys, Staten Isl, NY 10314 USA
[5] Princeton Univ, Dept Phys, Princeton, NJ 08544 USA
[6] Tech Univ Munich, Walter Schottky Inst, Dept Phys, D-85748 Garching, Germany
[7] Tech Univ Munich, Inst Adv Study, D-85748 Garching, Germany