1. Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA
2. Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom
3. Department of Physics, University College Cork, Cork T12 K8AF, Ireland
4. Department of Applied Physics, Stanford University, Stanford, California 94305, USA
5. Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA;
6. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
7. Department of Physics, Stanford University, Stanford, California 94305, USA
8. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
9. Department of Physics and Center for Theory of Quantum Matter, University of Colorado, Boulder, Colorado 80309, USA
10. Condensed Matter Physics & Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
11. Department of Physics, University of Florida, Gainesville, Florida 32611, USA