1. Institute of Physics, Nicolaus Copernicus University in Toruń , Grudziadzka 5 , Toruń 87-100 , Poland
2. Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology (KIT) , Karlsruhe 76131 , Germany
3. Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology , College Park 20742 , MD , USA
4. Nanoscale Device Characterization Division, National Institute of Standards and Technology , Gaithersburg 20899 , MD , USA
5. Centro de Física de Materiales, CFM-MPC CSIC-UPV/EHU , Paseo Manuel Lardizabal 5 , Donostia-San Sebastián 20018 , Spain
6. Donostia International Physics Center (DIPC) , Paseo Manuel Lardizabal 4 , Donostia-San Sebastián 20018 , Spain
7. Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT) , Karlsruhe 76021 , Germany