1. A.F. Ioffe Physico-Technical Institute RAS, 194021 St. Petersburg, Russia
2. National High Magnetic Field Laboratory, Los Alamos, New Mexico 87545, USA
3. Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland
4. Laboratoire d'Optique, Ecole Supérieure de Physique et Chimie Industrielles, 10 rue Vauquelin, 75005 Paris, France