1. Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
2. Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
3. Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
4. Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
5. IBM T.J. Watson Research Center, Yorktown Heights, New York 10598, USA