1. Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden), 01069 Dresden, Germany
2. Institute of Materials Science, Dresden University of Technology (TU Dresden), 01062 Dresden, Germany
3. Fraunhofer Institute for Integrated Systems and Device Technology, 91058 Erlangen, Germany
4. Faculty of Physics, Bielefeld University, 33615 Bielefeld, Germany