1. Physicotechnical Low-Temperature Institute of B.I. Verkin, NAN Ukrainy, pr. Nauk, 47, Khar'kov 61103, Ukraine and V.N. Karazin Khar'kov National University, pl. Svobody, 4, Khar'kov 61077, Ukraine
2. Physicotechnical Low-Temperature Institute of B.I. Verkin, NAN Ukrainy, pr. Nauk, 47, Khar'kov 61103, Ukraine