[1] Tech Univ Munich, Walter Schottky Inst, D-85748 Garching, Germany
[2] Tech Univ Munich, Dept Phys, D-85748 Garching, Germany
[3] TU Dortmund, D-44221 Dortmund, Germany
[4] Univ Augsburg, Lehrstuhl Expt Phys 1, D-86159 Augsburg, Germany
[5] Univ Augsburg, Augsburg Ctr Innovat Technol ACIT, D-86159 Augsburg, Germany
[6] Univ Fed Uberlandia, Inst Fis, BR-38400902 Uberlandia, MG, Brazil