1. Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544;
2. Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada;
3. Quantum Materials Program, Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
4. Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, New York 13902;