1. Attocube systems AG, Königinstraße 11a, 80539 Munich, Germany
2. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305-4045, USA
3. Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008-5252, USA
4. Geballe Laboratory for Advanced Materials and Department of Applied Physics, Stanford University, Stanford, California 94305-4045, USA
5. Department of Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305-4045, USA
6. IBM Research Division, T.J. Watson Research Center, Yorktown Heights, New York 10598, USA
7. OcteVue, Hadley, Massachusetts 01035, USA
8. Department of Applied Physics, Department of Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305-4045, USA