[1] Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
[2] Institute of Physical Chemistry, University of Heidelberg, D-69120 Heidelberg, Germany
[3] Infineon Technologies AG, Balanstr. 73, D-81541 Munich, Germany
[4] B. Verkin Inst. Low Temp. Phys./Eng., Ukrainean Academy of Sciences, 310164 Kharkov, Ukraine
[5] General Physics Institute, 117942 Moscow, Russia