1. Laboratory of Atomic and Solid-State Physics, Cornell University, Ithaca, New York 14853, USA
2. Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
3. School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
4. Laboratory of Quantum Materials (QMAT), Institute of Materials, École Polytechnique Fédéral de Lausanne (EPFL), 1015 Lausanne, Switzerland
5. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA