[1] Carl von Ossietzky Univ Oldenburg, Inst Phys, D-26129 Oldenburg, Germany
[2] Carl von Ossietzky Univ Oldenburg, Ctr Nanoscale Dynam CENAD, D-26129 Oldenburg, Germany
[3] Carl von Ossietzky Univ Oldenburg, Inst Biol, D-26129 Oldenburg, Germany
[4] Philipps Univ Marburg, Fachbereich Phys, D-35032 Marburg, Germany
[5] Carl von Ossietzky Univ Oldenburg, Res Ctr Neurosensory Sci, D-26129 Oldenburg, Germany