[1] Univ Basque Country, Dept Fis Mat, San Sebastian 20080, Spain
[2] UPJS, Fac Sci, Kosice 04154, Slovakia
[3] Slovak Acad Sci, Ctr Low Temp Phys, Inst Expt Phys, SK-04001 Kosice, Slovakia
[4] Safarik Univ, SK-04001 Kosice, Slovakia
[5] Tech Univ Kosice, FEEL, Dept Phys, Kosice, Slovakia