1. Department of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
2. Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden, Germany
3. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia
4. Lobachevsky State University of Nizhni Novgorod, Nizhny Novgorod 603950, Russia