1. St. Petersburg State Polytechnical University, Polytechnicheskaya 29, St. Petersburg 195251, Russia
2. Ioffe Physico-Technical Institute, Polytechnicheskaya 26, St. Petersburg 194021, Russia
3. International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, 53-421 Wroclaw, Poland
4. Leibniz University of Hannover, ETP, Wilhelm-Busch-Street, 30167 Hannover, Germany