1. Department of Physics, New York University, New York, NY 10003, USA.
2. Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA.
3. Department of Chemistry, New York University, New York, NY 10003, USA.
4. Département de Physique, Ecole Normale Supérieure de Lyon, 69007 Lyon, France.
5. Center for Neural Science, New York University, New York, NY 10003, USA.
6. School of Materials Science and Engineering, College of Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.