1. Kirchhoff-Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany
2. Institute for Data Processing and Electronics, Karlsruher Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
3. Institute of Micro- and Nanoelectronic Systems, Karlsruher Institute of Technology, Hertzstraße 16, 76187 Karlsruhe, Germany