1. 2nd Institute of Physics and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany
2. Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
3. Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
4. Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany
5. JARA-FIT Institute for Quantum Information, Forschungszentrum Jülich GmbH and RWTH Aachen University, 52074 Aachen, Germany