Ultrasonic attenuation in a type II superconducting alloy

Ultrasonic attenuation measurements have now been obtained on a magnetically reversible type-II superconductor with both a high Ginzburg-Landau parameter (κ_g > 1) and with BCS coherence length > electronic mean free path. For applied fields close to H_c2, the data appear to agree with dirty-limit (ξ₀/l > 1) theory which predicts a linear dependence of α on H. At fields farther from H_c2, α(H) deviates from linearity and appears to fit empirically to a parabolic function of H. At very low fields, H {greater-than or approximate} H_c1, the H- and T-dependence is in apparent agreement with another theory. Physical insight into the behavior in this region could be obtained with a model in which vortices are replaced by cylinders of completely normal material imbedded in a superconducting matrix.