1. Institute of Experimental Physics, University of Wrocław, Pl. M. Borna 9, 50-204 Wrocław, Poland
2. Faculty of Physics, Vilnius University, Sauletekio Aleja 9, 2054 Vilnius, Lithuania
3. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław 2, Poland