1. Department of Physics, University of Washington, Seattle, WA 98195, USA.
2. 3. Physikalisches Institut, University of Stuttgart, 70569 Stuttgart, Germany.
3. Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
4. Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
5. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
6. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
7. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
8. Center for Applied Quantum Technology, University of Stuttgart, 70569 Stuttgart, Germany.
9. Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.