1. Ulyanovsk State UniversityUlyanovsk 432000Russia
2. Donetsk Institute for Physics and Engineering, named after O.O. Galkin, of the National Academy of Sciences of UkraineKyiv 03680Ukraine
3. Faculty of Physics, V. N. Karazin Kharkiv National UniversityKharkiv 61000Ukraine
4. Faculty of Physics, Adam Mickiewicz UniversityPoznan 61614Poland
5. Depto. Física de Materiales, Universidad del País Vasco, UPV/EHUSan Sebastian 20018Spain
6. IKERBASQUE, The Basque Foundation for ScienceBilbao 48013Spain