[1] Univ Wurzburg Hubland, Expt Phys 2, Phys Inst, D-97074 Wurzburg, Germany
[2] Russian Acad Sci, Siberian Branch, VS Sobolev Inst Geol & Mineral, Novosibirsk 630090, Russia
[3] Novosibirsk State Univ, Dept Phys, Novosibirsk 630090, Russia
[4] St Petersburg State Univ, St Petersburg 198504, Russia
[5] Russian Acad Sci, Siberian Branch, AV Rzanov Inst Semicond Phys, Novosibirsk 630090, Russia
[6] Wilhelm Conrad Rontgen Ctr Complex Mat Syst RCCM, D-97074 Wurzburg, Germany