Ultrasonic Attenuation Measurements on Single Crystal of V₃Si near T_c

Abstract

The normal and the superconducting states of a single crystal V₃Si were studied by the usual pulse-echo method of ultrasonics at about 100 MHz. The magnetic field dependence of the ultrasonic attenuation slightly below T_c showed a complicated behavior characterized by four critical fields, which indicated the mixture of cubic and tetragonal phases. It was found that the critical temperature in the tetragonal phase T_c(Tet.) should be a little bit (∼0.1 K) lower than that in the cubic phase T_c(Cub.). It was also found that both the second critical fields H_c2(Cub.) and H_c2(Tet.) showed a linear ΔT (≡T_c−T)-dependence in the same way as those of usual type-II superconductors. The ratio of the H_c2(Tet.) to the H_c2(Cub.) was about 0.84, which may correspond to the ratio of the Fermi velocity in the cubic phase to that in the tetragonal phase. From the temperature dependence of the critical attenuations Δα, the values of the ultrasonic attenuation at each critical field, we obtained a formula as Δα(Tet.)∝(ΔT)^2⁄3.